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Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolita ...
is in the
midwestern United States The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four census regions of the United States Census Bureau (also known as "Region 2"). It occupies the northern central part of the United States. I ...
. Surrounding states are
Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...
to the north,
Iowa Iowa () is a state in the Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wisconsin to the northeast, Illinois to the ...
and
Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...
to the west,
Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia to ...
to the east and south, and
Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...
to the east. Illinois also borders
Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and the ...
, but only via a northeastern water boundary in
Lake Michigan Lake Michigan is one of the five Great Lakes of North America. It is the second-largest of the Great Lakes by volume () and the third-largest by surface area (), after Lake Superior and Lake Huron. To the east, its basin is conjoined with that o ...
. Nearly the entire western boundary of Illinois is the
Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...
, except for a few areas where the river has changed course. Illinois' southeastern and southern boundary is along the
Wabash River The Wabash River ( French: Ouabache) is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed May 13, 2011 river that drains most of the state of Indiana in the United States. It flows fro ...
and the
Ohio River The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illino ...
, whereas its northern boundary and much of its eastern boundary are straight survey (longitudinal and latitudinal) lines. Illinois has a maximum north–south distance of 390 miles (630 km) and 210 miles (340 km) east-west. Its total area is .


Statistics

*Illinois has a maximum north–south distance of and east-west. *Total area is , ranked 25th in size of the 50 states. *Water area is ;
Lake Michigan Lake Michigan is one of the five Great Lakes of North America. It is the second-largest of the Great Lakes by volume () and the third-largest by surface area (), after Lake Superior and Lake Huron. To the east, its basin is conjoined with that o ...
accounts for most of this. *
Charles Mound Charles Mound is a gentle, high hill located in Scales Mound Township, Jo Daviess County, Illinois, United States. It is northeast of the small town of Scales Mound, and northeast of Galena. Despite its name, Charles Mound is a naturally occ ...
in the northwest
Driftless Area The Driftless Area, a topographical and cultural region in the American Midwest, comprises southwestern Wisconsin, southeastern Minnesota, northeastern Iowa, and the extreme northwestern corner of Illinois. Never covered by ice during the las ...
is the highest point in the state at above sea level. *The
Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...
at Cairo, Illinois is the lowest point, at . *Average elevation is above sea level. * McLean County is the largest county in terms of land area (1,184 sq mi.), while
Cook County Cook County is the most populous county in the U.S. state of Illinois and the second-most-populous county in the United States, after Los Angeles County, California. More than 40% of all residents of Illinois live within Cook County. As of 20 ...
is the largest county in terms of population (5,275,541 as of 2020), and the largest when land and water area are combined.


Geographical divisions

Illinois has three major geographical divisions: Northern, Central, and Southern. Collectively, central and southern Illinois are often referred to within Illinois as "
downstate Illinois Downstate Illinois refers to the part of the U.S. state of Illinois south of the Chicago metropolitan area, which is in the northeast corner of the state and has been dominant in American history, politics, and culture. It is defined as the part ...
" but with political developments since World War II "Downstate" now generally refers to ''all'' of Illinois outside of the Chicago metro area.


Northern Illinois

Northern Illinois Northern Illinois is a region generally covering the northern third of the U.S. state of Illinois. The region is by far the most populous of Illinois with nearly 9.7 million residents as of 2010. Economics Northern Illinois is dominated by t ...
is dominated by the
Chicago metropolitan area The Chicago metropolitan area, also colloquially referred to as Chicagoland, is a metropolitan area in the Midwestern United States. Encompassing 10,286 sq mi (28,120 km2), the metropolitan area includes the city of Chicago, its suburbs and hi ...
, including the city of
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...
, its suburbs, and the adjoining exurban area into which the metropolis is expanding. The "
collar counties Collar counties is a colloquialism for DuPage, Kane, Lake, McHenry, and Will counties, the five counties of Illinois that border Cook County, which is home to Chicago. The collar counties are part of the Chicago metropolitan area and comp ...
" are the five counties that surround the centrally located Cook County in the Chicago metropolitan area: DuPage County, Kane County, Lake County, McHenry County, and Will County. The term "
Chicagoland The Chicago metropolitan area, also colloquially referred to as Chicagoland, is a metropolitan area in the Midwestern United States. Encompassing 10,286 sq mi (28,120 km2), the metropolitan area includes the city of Chicago, its suburbs and hint ...
" is sometimes used to describe the metro area, including Chicago, its suburbs within Cook County, and the so-called collar counties. The term is said to have been coined by ''
Chicago Tribune The ''Chicago Tribune'' is a daily newspaper based in Chicago, Illinois, United States, owned by Tribune Publishing. Founded in 1847, and formerly self-styled as the "World's Greatest Newspaper" (a slogan for which WGN radio and television ar ...
'' publisher
Robert R. McCormick Robert Rutherford "Colonel" McCormick (July 30, 1880 – April 1, 1955) was an American lawyer, businessman and anti-war activist. A member of the McCormick family of Chicago, McCormick became a lawyer, Republican Chicago alderman, distinguish ...
. The
Chicagoland Chamber of Commerce The Chicagoland Chamber of Commerce is a non-profit organization promoting business in the Chicago metropolitan area The Chicago metropolitan area, also colloquially referred to as Chicagoland, is a metropolitan area in the Midwestern United ...
defines it as all of Cook, and DuPage, Kane, Lake, McHenry and Will counties. The region is cosmopolitan, densely populated, industrialized, and settled by a wide variety of ethnic groups. As defined by the federal government, the Chicago Metropolitan Area includes two counties in Indiana, two counties in Wisconsin, and the following 11 counties in Illinois:
Cook Cook or The Cook may refer to: Food preparation * Cooking, the preparation of food * Cook (domestic worker), a household staff member who prepares food * Cook (professional), an individual who prepares food for consumption in the food industry * ...
,
DeKalb DeKalb or De Kalb may refer to: People * Baron Johann de Kalb (1721–1780), major general in the American Revolutionary War Places Municipalities in the United States * DeKalb, Illinois, the largest city in the United States named DeKalb **DeKal ...
, DuPage, Grundy, Kane, Kankakee, Kendall,
Lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
, LaSalle, McHenry, and
Will Will may refer to: Common meanings * Will and testament, instructions for the disposition of one's property after death * Will (philosophy), or willpower * Will (sociology) * Will, volition (psychology) * Will, a modal verb - see Shall and will ...
counties. The
Rockford Metropolitan Area The Rockford Metropolitan Statistical Area, as defined by the United States Census Bureau, is an area consisting of four counties in north-central Illinois, anchored by the city of Rockford. As of the 2010 census, the MSA had a population of ...
is north-central near
Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...
, on the Rock River. The
Quad Cities Metropolitan Area The Quad Cities metropolitan area, more formally known as the Davenport–Moline–Rock Island Metropolitan Statistical Area, is the metropolitan area associated with the Quad Cities in the U.S. states of Iowa and Illinois. The area consists of t ...
is on both sides of the
Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...
separating Illinois from
Iowa Iowa () is a state in the Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wisconsin to the northeast, Illinois to the ...
. The Illinois side includes Henry County, Mercer County, and
Rock Island County Rock Island County is a county located in the U.S. state of Illinois, bounded on the west by the Mississippi River. According to the 2010 census, it had a population of 147,546. Its county seat is Rock Island; its largest city is neighboring ...
. In extreme northwestern Illinois the
Driftless Zone The Driftless Area, a topographical and cultural region in the American Midwest, comprises southwestern Wisconsin, southeastern Minnesota, northeastern Iowa, and the extreme northwestern corner of Illinois. Never covered by ice during the Last G ...
, a region of unglaciated and therefore higher and more
rugged topography ''Rugged'' is a 2019 Indian Kannada-language romantic action film Romance films or movies involve romantic love stories recorded in visual media for broadcast in theatres or on television that focus on passion, emotion, and the affectionate ...
, occupies a small part of the state.
Charles Mound Charles Mound is a gentle, high hill located in Scales Mound Township, Jo Daviess County, Illinois, United States. It is northeast of the small town of Scales Mound, and northeast of Galena. Despite its name, Charles Mound is a naturally occ ...
, located in this region, is the state's highest elevation above
sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...
.


Central Illinois

Southward and westward, the second major division is
Central Illinois Central Illinois is a region of the U.S. state of Illinois that consists of the entire central third of the state, divided from north to south. Also known as the ''Heart of Illinois'', it is characterized by small towns and mid-sized cities. Agri ...
, an area of mostly flat
prairie Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the ...
with the exception of areas along the Illinois and Mississippi rivers that are steeped in hills and bluffs hanging high above the rivers providing commanding views for miles. The western section (west of the Illinois River) was originally part of the
Military Tract of 1812 Shortly before the War of 1812, congress passed Military Tract of 1812. This allowed for quarter-sections of land to be promised to those enlisting to fight against the British. This encouraged both enlistment and later settlement, although many so ...
and forms the distinctive western bulge of state. Central Illinois is characterized by small towns and mid-sized cities. Agriculture, particularly
corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...
and soybeans, figures prominently. Major cities include Peoria, and Springfield (the state capital). The Champaign-Urbana Metropolitan Area is located in the central region of the state and is composed of
Champaign Champaign ( ) is a city in Champaign County, Illinois, United States. The population was 88,302 at the 2020 census. It is the tenth-most populous municipality in Illinois and the fourth most populous city in Illinois outside the Chicago metropo ...
,
Ford Ford commonly refers to: * Ford Motor Company, an automobile manufacturer founded by Henry Ford * Ford (crossing), a shallow crossing on a river Ford may also refer to: Ford Motor Company * Henry Ford, founder of the Ford Motor Company * Ford F ...
, and Piatt counties.


Southern Illinois

The third division is
Southern Illinois Southern Illinois, also known as Little Egypt, is the southern third of Illinois, principally along and south of Interstate 64. Although part of a Midwestern state, this region is aligned in culture more with that of the Upland South than the Mi ...
, comprising the area south of
U.S. Route 50 U.S. Route 50 or U.S. Highway 50 (US 50) is a major east–west route of the U.S. Highway system, stretching from Interstate 80 (I-80) in West Sacramento, California, to Maryland Route 528 (MD 528) in Ocean City, Maryland, on the Atlanti ...
, and including Little Egypt, near the juncture of the
Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...
and
Ohio River The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illino ...
. This region can be distinguished from the other two by its warmer climate, different mix of crops (including
cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus ''Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor perce ...
farming in the past), more rugged unglaciated topography, as well as small-scale oil deposits and
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...
mining. The population in southern Illinois is concentrated in two areas: *
Metro-East Metro East is a region in southern Illinois that contains eastern and northern suburbs and exurbs of St. Louis, Missouri, United States. It encompasses five Southern Illinois counties (and parts of three others) in the St. Louis Metropolitan Sta ...
is an area east of
St. Louis St. Louis () is the second-largest city in Missouri, United States. It sits near the confluence of the Mississippi and the Missouri Rivers. In 2020, the city proper had a population of 301,578, while the bi-state metropolitan area, which e ...
and it includes
Jersey Jersey ( , ; nrf, Jèrri, label=Jèrriais ), officially the Bailiwick of Jersey (french: Bailliage de Jersey, links=no; Jèrriais: ), is an island country and self-governing Crown Dependencies, Crown Dependency near the coast of north-west F ...
,
Madison Madison may refer to: People * Madison (name), a given name and a surname * James Madison (1751–1836), fourth president of the United States Place names * Madison, Wisconsin, the state capital of Wisconsin and the largest city known by this ...
, St. Clair, Macoupin, and parts of
Bond Bond or bonds may refer to: Common meanings * Bond (finance), a type of debt security * Bail bond, a commercial third-party guarantor of surety bonds in the United States * Chemical bond, the attraction of atoms, ions or molecules to form chemica ...
and
Calhoun John C. Calhoun (1782–1850) was the 7th vice president of the United States. Calhoun can also refer to: Surname * Calhoun (surname) Inhabited places in the United States *Calhoun, Georgia *Calhoun, Illinois * Calhoun, Kansas * Calhoun, Kentuc ...
from the St. Louis Metropolitan Statistical Area, as well as
Clinton County Clinton County may refer to: *Counties named for George Clinton, first and third Governor of New York, and later the fourth Vice President of the United States: **Clinton County, New York ** Clinton County, Ohio *Counties named for DeWitt Clinton, ...
.State of Illinois
Metro-East "Metro East: 1965 to Today", Illinois Labor Market Review
* Carbondale, Marion, West Frankfort, Benton, Herrin, Murphysboro, Carterville, and the Johnston City area. The
Shawnee Hills The Shawnee Hills is a region of southern Illinois that rests mainly in an east-west arc roughly following the outline of the southern end of the Illinois Basin. Whereas Mississippian and Pennsylvania Age rock layers are deep beneath the soil su ...
arise in southern Illinois.
Illinoian Stage The Illinoian Stage is the name used by Quaternary geologists in North America to designate the period c.191,000 to c.130,000 years ago, during the middle Pleistocene, when sediments comprising the Illinoian Glacial Lobe were deposited. It precedes ...
, about 132,000 to 300,000 years before present, climbed the northern face of the Shawnee Hills, but did not reach the summit. Most of the Shawnee Hills is therefore unglaciated. The floodplain on the Mississippi River from
Alton Alton may refer to: People *Alton (given name) *Alton (surname) Places Australia *Alton National Park, Queensland * Alton, Queensland, a town in the Shire of Balonne Canada * Alton, Ontario *Alton, Nova Scotia New Zealand * Alton, New Zealand, ...
to the
Kaskaskia River The Kaskaskia River is a tributary of the Mississippi River, approximately long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map , accessed May 13, 2011 in central and southern Illinois in the Un ...
is the
American Bottom The American Bottom is the flood plain of the Mississippi River in the Metro-East region of Southern Illinois, extending from Alton, Illinois, south to the Kaskaskia River. It is also sometimes called "American Bottoms". The area is about , mo ...
, and is the site of the ancient city of
Cahokia The Cahokia Mounds State Historic Site ( 11 MS 2) is the site of a pre-Columbian Native American city (which existed 1050–1350 CE) directly across the Mississippi River from modern St. Louis, Missouri. This historic park lies in south- ...
, and was a region of early French settlement, as well as the site of the first state capital, at
Kaskaskia The Kaskaskia were one of the indigenous peoples of the Northeastern Woodlands. They were one of about a dozen cognate tribes that made up the Illiniwek Confederation, also called the Illinois Confederation. Their longstanding homeland was in t ...
. The extreme southern tip of Illinois is in the
Gulf Coastal Plain The Gulf Coastal Plain extends around the Gulf of Mexico in the Southern United States and eastern Mexico. This coastal plain reaches from the Florida Panhandle, southwest Georgia, the southern two-thirds of Alabama, over most of Mississippi, wes ...
.


Political geography

The city of Chicago and some of its older suburbs are heavily Democratic. While this tendency has historically been balanced by
Republican Republican can refer to: Political ideology * An advocate of a republic, a type of government that is not a monarchy or dictatorship, and is usually associated with the rule of law. ** Republicanism, the ideology in support of republics or agains ...
voters in the suburbs, Democrats have significantly increased their suburban support in the past decade. Central Illinois's largely rural character helps to sustain a largely Republican voting pattern and widespread antipathy toward Chicago. The combination of poorer soil, coal mining and industrialization has caused the southern region to lean Democratic politically, especially in the urbanized region around Saint Louis,
Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...
.
Rockford, Illinois Rockford is a city in Winnebago County, Illinois, located in the far northern part of the state. Situated on the banks of the Rock River, Rockford is the county seat of Winnebago County (a small portion of the city is located in Ogle County). ...
is known as a center of liberal "gypsy moth" Republicans.


Geology

Illinois is predominantly covered with soil, hundreds of feet thick in many places. Much of this soil is called, appropriately, "
Illite Illite is a group of closely related non-expanding clay minerals. Illite is a secondary mineral precipitate, and an example of a phyllosilicate, or layered alumino-silicate. Its structure is a 2:1 sandwich of silica tetrahedron (T) – alumina ...
", and is the most common type of soil on the planet. The visible geology of the state is mainly
Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
, with rocks buried deeply. The wealth of the state mainly arises from this abundance of soil and the favorable agrarian conditions it provides. Illinois is a major
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...
-producing state. Much of the bedrock surface is of Pennsylvanian age, including "cyclothemes", regular sequences of limestone, shale and coal layers. Newer rocks may have once existed in the State, but these have been removed by repeated epochs of glaciation. Only tiny areas of newer bedrock exist. The chance of finding dinosaur bones in Illinois is almost nil:, the Pennsylvanian rocks were here before the dinosaurs.
Galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It cryst ...
, a
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
ore, has been mined in the northwest corner of the state. The ore was processed around Peru, Illinois, where river transport was available to bring the ore to a source of coal. About six tons of coal are needed for each ton of ore.
Fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...
,
calcium fluoride Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white insoluble solid. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing to impurities. ...
, is the state mineral. It is mined in the southeastern portion of the state, around
Metropolis A metropolis () is a large city or conurbation which is a significant economic, political, and cultural center for a country or region, and an important hub for regional or international connections, commerce, and communications. A big c ...
. Fluorine gas is produced from fluorite. This is used in the production of
uranium hexafluoride Uranium hexafluoride (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...
in Metropolis, Illinois for use at the
gaseous diffusion Gaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride (UF6) through semipermeable membranes. This produces a slight separation between the molecules containing uranium-235 (235U) and uranium-2 ...
plant in
Paducah, Kentucky Paducah ( ) is a home rule-class city in and the county seat of McCracken County, Kentucky. The largest city in the Jackson Purchase region, it is located at the confluence of the Tennessee and the Ohio rivers, halfway between St. Louis, Missour ...
.
Geode A geode (; ) is a geological secondary formation within sedimentary and volcanic rocks. Geodes are hollow, vaguely spherical rocks, in which masses of mineral matter (which may include crystals) are secluded. The crystals are formed by the fill ...
s can be found in the older Mississippian outcroppings along the
Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...
.
Igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...
intrusions are found in the far southern areas of the State. Ages ago North America began to split roughly along the lines of the Ohio and Mississippi Rivers. Igneous rock flowed up into fissures, as a new ocean began to form. Had this continued, Illinois might have resembled the
Arabian Peninsula The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate ...
, a broken terrain between two continents. This split, however, failed: the continent reclosed, leaving only a few igneous intrusions, and some oil fields, as evidence that it happened. North of the
Illinois River The Illinois River ( mia, Inoka Siipiiwi) is a principal tributary of the Mississippi River and is approximately long. Located in the U.S. state of Illinois, it has a drainage basin of . The Illinois River begins at the confluence of the D ...
the bedrock surface is much older
Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...
sandstone. This sandstone yields ancient sand that is very useful in the production of glass, and in making molds for metal castings.


Coal

The majority of Illinois surface
bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...
belongs to the Pennsylvanian period, particularly the downstate region. About 68% of the state has
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...
-bearing strata of this geologic period. According to the Illinois State Geological Survey, 211 billion tons of
bituminous coal Bituminous coal, or black coal, is a type of coal containing a tar-like substance called bitumen or asphalt. Its coloration can be black or sometimes dark brown; often there are well-defined bands of bright and dull material within the seams. It ...
are estimated to lie under the surface, having a total heating value greater than the estimated oil deposits in the
Arabian Peninsula The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate ...
. However, this coal has a high
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
content and as such requires special equipment to reduce air pollution.


Rivers

Illinois is mainly bounded by rivers, and the
Illinois River The Illinois River ( mia, Inoka Siipiiwi) is a principal tributary of the Mississippi River and is approximately long. Located in the U.S. state of Illinois, it has a drainage basin of . The Illinois River begins at the confluence of the D ...
bisects the state. A few rivers, including the
Fox Foxes are small to medium-sized, omnivorous mammals belonging to several genera of the family Canidae. They have a flattened skull, upright, triangular ears, a pointed, slightly upturned snout, and a long bushy tail (or ''brush''). Twelve sp ...
and
Rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...
Rivers enter the State from Wisconsin. The
Iroquois The Iroquois ( or ), officially the Haudenosaunee ( meaning "people of the longhouse"), are an Iroquoian-speaking confederacy of First Nations peoples in northeast North America/ Turtle Island. They were known during the colonial years to ...
and Kankakee arise in
Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...
, but lose their identity before reaching the
Mississippi Mississippi () is a state in the Southeastern region of the United States, bordered to the north by Tennessee; to the east by Alabama; to the south by the Gulf of Mexico; to the southwest by Louisiana; and to the northwest by Arkansas. Miss ...
. The North Fork of the Vermilion River arises in Indiana, but joins the
Vermilion Vermilion (sometimes vermillion) is a color, color family, and pigment most often made, since ancient history, antiquity until the 19th century, from the powdered mineral cinnabar (a form of mercury sulfide, which is toxic) and its correspondi ...
, which exits the state before joining the
Wabash River The Wabash River ( French: Ouabache) is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed May 13, 2011 river that drains most of the state of Indiana in the United States. It flows fro ...
in Indiana. Other rivers include the
Ohio River The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illino ...
, the
Kaskaskia River The Kaskaskia River is a tributary of the Mississippi River, approximately long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map , accessed May 13, 2011 in central and southern Illinois in the Un ...
, the
Sangamon River The Sangamon River is a principal tributary of the Illinois River, approximately long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed May 13, 2011 in central Illinois in the United Stat ...
and the
Chicago River The Chicago River is a system of rivers and canals with a combined length of that runs through the city of Chicago, including its center (the Chicago Loop). Though not especially long, the river is notable because it is one of the reasons for ...
. The Cashe River area in southern Illinois forms the basis for a
Ramsar Convention The Ramsar Convention on Wetlands of International Importance Especially as Waterfowl Habitat is an international treaty for the conservation and sustainable use of Ramsar sites (wetlands). It is also known as the Convention on Wetlands. It i ...
Wetland of International Importance.


Groundwater

Subsurface water is generally plentiful in Illinois. However, irregular gravel deposits from glaciation can lead to difficulties predicting depth of the water table. The Mahomet Aquifer is a large aquifer used as a source for public water supply by many communities in Central Illinois.


Flora and fauna

Large
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
species currently found in Illinois include
whitetail deer The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...
and
coyote The coyote (''Canis latrans'') is a species of canis, canine native to North America. It is smaller than its close relative, the wolf, and slightly smaller than the closely related eastern wolf and red wolf. It fills much of the same ecologica ...
, with the latter becoming urbanized in the
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...
area, as well as common in the rural areas. Furbearers commonly found include
opossum Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 93 species in 18 genera. Opossums originated in South America and entered North ...
,
raccoon The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of ...
,
mink Mink are dark-colored, semiaquatic, carnivorous mammals of the genera ''Neogale'' and '' Mustela'' and part of the family Mustelidae, which also includes weasels, otters, and ferrets. There are two extant species referred to as "mink": the A ...
,
red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...
and
gray fox The gray fox (''Urocyon cinereoargenteus''), or grey fox, is an omnivorous mammal of the family Canidae, widespread throughout North America and Central America. This species and its only congener, the diminutive island fox (''Urocyon littor ...
es, and muskrat. Commonly seen lagomorphs include the
cottontail rabbit Cottontail rabbits are the leporid species in the genus ''Sylvilagus'', found in the Americas. Most ''Sylvilagus'' species have stub tails with white undersides that show when they retreat, giving them their characteristic name. However, this ...
and commonly seen rodents include squirrels. Game birds found include
Canada goose The Canada goose (''Branta canadensis''), or Canadian goose, is a large wild goose with a black head and neck, white cheeks, white under its chin, and a brown body. It is native to the arctic and temperate regions of North America, and it is o ...
,
mallard duck The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa, and has been introduced species, introduced to New Zealand, Australia, Peru, Bra ...
,
ruffed grouse The ruffed grouse (''Bonasa umbellus'') is a medium-sized grouse occurring in forests from the Appalachian Mountains across Canada to Alaska. It is the most widely distributed game bird in North America. It is non-migratory. It is the only specie ...
,
wild turkey The wild turkey (''Meleagris gallopavo'') is an Upland game bird, upland ground bird native to North America, one of two extant species of Turkey (bird), turkey and the heaviest member of the order Galliformes. It is the ancestor to the domestic ...
, and
bobwhite quail The northern bobwhite (''Colinus virginianus''), also known as the Virginia quail or (in its home range) bobwhite quail, is a ground-dwelling bird native to Canada, the United States, Mexico, and Cuba, with introduced populations elsewhere in th ...
. The
northern cardinal The northern cardinal (''Cardinalis cardinalis'') is a bird in the genus ''Cardinalis''; it is also known colloquially as the redbird, common cardinal, red cardinal, or just cardinal (which was its name prior to 1985). It can be found in southea ...
is the official state bird. The state has approximately 300 species of birds, many of which migrate on the
Mississippi Flyway The Mississippi Flyway is a bird migration route that generally follows the Mississippi, Missouri, and Lower Ohio Rivers in the United States across the western Great Lakes to the Mackenzie River and Hudson Bay in Canada. The main endpoints of ...
. Extensive wetland restoration along the
Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...
and
Illinois River The Illinois River ( mia, Inoka Siipiiwi) is a principal tributary of the Mississippi River and is approximately long. Located in the U.S. state of Illinois, it has a drainage basin of . The Illinois River begins at the confluence of the D ...
are attracting many species. About two thirds of the state was originally prairie, with much of the area converted to rowcrop farming, while the southern third of the state remains heavily forested with
oak An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...
,
hickory Hickory is a common name for trees composing the genus ''Carya'', which includes around 18 species. Five or six species are native to China, Indochina, and India (Assam), as many as twelve are native to the United States, four are found in Mexi ...
, and
maple ''Acer'' () is a genus of trees and shrubs commonly known as maples. The genus is placed in the family Sapindaceae.Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 nd more or less continuously updated since http ...
. Also, several prairie plants. Especially in the northern third of the state,
intensive agriculture Intensive agriculture, also known as intensive farming (as opposed to extensive farming), conventional, or industrial agriculture, is a type of agriculture, both of crop plants and of animals, with higher levels of input and output per unit of ag ...
has made some species rare, while population numbers are increasing in the less-developed south. Large mammals generally no longer found in the wild in Illinois include
American bison The American bison (''Bison bison'') is a species of bison native to North America. Sometimes colloquially referred to as American buffalo or simply buffalo (a different clade of bovine), it is one of two extant species of bison, alongside the ...
, gray wolf,
American black bear The American black bear (''Ursus americanus''), also called simply a black bear or sometimes a baribal, is a medium-sized bear endemic to North America. It is the continent's smallest and most widely distributed bear species. American black bear ...
, and
elk The elk (''Cervus canadensis''), also known as the wapiti, is one of the largest species within the deer family, Cervidae, and one of the largest terrestrial mammals in its native range of North America and Central and East Asia. The common ...
.


Climate

Illinois has a
continental climate Continental climates often have a significant annual variation in temperature (warm summers and cold winters). They tend to occur in the middle latitudes (40 to 55 north), within large landmasses where prevailing winds blow overland bringing som ...
, with large temperature extremes not moderated by either mountains or oceans. Weather is influenced primarily by cold Canadian Arctic air in the winter, and warm, humid air from the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...
in the summer. High temperatures in the south of the state are about 10 to 12 °F. warmer than the north. Average annual temperature is 47 °F. in the north and 58 °F. in the south. Temperatures greater than 90 °F. occur about 45 days per year in the south, and 12 days per year in the north. Temperatures below zero °F. occur one day or less per year in the south, and 12 days per year in the north. Annual rainfall is in the north and in the south. Prevailing
winds Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...
are from the west. Average wind speeds "blowing off the
prairie Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the ...
" are greater in the
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...
area. Statewide, the wind speeds average , and is greater in the winter than in summer. Snowfall averages in the north and in the south, although the actual snowfalls vary greatly by year. In some years, southern Illinois receives very little snowfall, and may never get typical winter weather. Most of the state has four distinct seasons. The southernmost part of the state is heavily forested and the trees are noted for having beautiful
fall Autumn, also known as fall in American English and Canadian English, is one of the four temperate seasons on Earth. Outside the tropics, autumn marks the transition from summer to winter, in September (Northern Hemisphere) or March ( Southe ...
colors.
Tornado A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, altho ...
es are a common hazard, primarily in the central part of the state, with peak months in June and April. Freezing rain is most common in central Illinois.


Border anomalies

The
Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...
is the nominal western boundary of the state, except for locations where the river has changed course. Kaskaskia, Illinois, the first state capital, is now west of the river. The Mississippi, due to a flood, destroyed the old town of Kaskaskia, and occupies what was the lower channel of the
Kaskaskia River The Kaskaskia River is a tributary of the Mississippi River, approximately long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map , accessed May 13, 2011 in central and southern Illinois in the Un ...
. A portion of
Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...
is east of the river, near
Grand Tower, Illinois Grand Tower is a city in Jackson County, Illinois, United States. The population was 605 at the 2010 census. The town gets its name from Tower Rock, a landmark island in the Mississippi River. History Former names of this town include ''La T ...
. Similar " avulsions" are found along the
Ohio River The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illino ...
border with
Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia to ...
and the
Wabash River The Wabash River ( French: Ouabache) is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed May 13, 2011 river that drains most of the state of Indiana in the United States. It flows fro ...
border with
Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...
.


See also

*
List of ecoregions in Illinois The list of ecoregions in Illinois are lists of terrestrial ecoregions (see also, ecosystem) of the United States' State of Illinois, as defined separately by the United States Environmental Protection Agency (USEPA), and by the World Wildlife Fu ...


Footnotes


Notes


References

* *


External links


About Illinois Data and Statistics
{{U.S. political divisions geographies