Jefferson County is a
county
A county () is a geographic region of a country used for administrative or other purposesL. Brookes (ed.) '' Chambers Dictionary''. Edinburgh: Chambers Harrap Publishers Ltd, 2005. in some nations. The term is derived from the Old French denoti ...
located in the
U.S. state
In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its so ...
of
Colorado
Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...
. As of the
2020 census, the population was 582,910,
making it the fourth-most populous county in Colorado. The
county seat
A county seat is an administrative center, seat of government, or capital city of a county or parish (administrative division), civil parish. The term is in use in five countries: Canada, China, Hungary, Romania, and the United States. An equiva ...
is
Golden,
and the most populous city is
Lakewood.
Jefferson County is included in the
Denver
Denver ( ) is a List of municipalities in Colorado#Consolidated city and county, consolidated city and county, the List of capitals in the United States, capital and List of municipalities in Colorado, most populous city of the U.S. state of ...
-
Aurora
An aurora ( aurorae or auroras),
also commonly known as the northern lights (aurora borealis) or southern lights (aurora australis), is a natural light display in Earth's sky, predominantly observed in high-latitude regions (around the Arc ...
-Lakewood, CO
Metropolitan Statistical Area. Located along the
Front Range
The Front Range is a mountain range of the Southern Rocky Mountains of North America located in the central portion of the U.S. State of Colorado, and southeastern portion of the U.S. State of Wyoming. It is the first mountain range encounter ...
of the
Rocky Mountains
The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...
, Jefferson County is adjacent to the state capital of Denver.
In 2010, the center of population of Colorado was located in Jefferson County.
The county's slogan is the "Gateway to the Rocky Mountains", and it is commonly nicknamed
Jeffco. The name Jeffco is incorporated in the name of the Jeffco School District, the Jeffco Business Center Metropolitan District No. 1, and several businesses located in Jefferson County. Jeffco is also incorporated in the unofficial monikers of many Jefferson County agencies. The
Rocky Mountain Metropolitan Airport operated by Jefferson County was previously known as the Jeffco Airport.
A major employer in Jefferson County is the large
Coors Brewing Company
The Coors Brewing Company is an American brewery and beer company based in Golden, Colorado, that was founded in 1873. In 2005, Adolph Coors Company, the holding company that owned Coors Brewing, merged with Molson, Inc. to become Molson Coor ...
in Golden. Also, the state-supported
Colorado School of Mines
The Colorado School of Mines (Mines) is a public research university in Golden, Colorado, United States. Founded in 1874, the school offers both undergraduate and graduate degrees in engineering, science, and mathematics, with a focus on ener ...
, a university specializing in
mining
Mining is the Resource extraction, extraction of valuable geological materials and minerals from the surface of the Earth. Mining is required to obtain most materials that cannot be grown through agriculture, agricultural processes, or feasib ...
,
geology
Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...
,
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...
, and
engineering
Engineering is the practice of using natural science, mathematics, and the engineering design process to Problem solving#Engineering, solve problems within technology, increase efficiency and productivity, and improve Systems engineering, s ...
is located in Jefferson County.
History
On August 25, 1855, the
Kansas Territorial Legislature created
Arapahoe County to govern the entire western portion of the
territory
A territory is an area of land, sea, or space, belonging or connected to a particular country, person, or animal.
In international politics, a territory is usually a geographic area which has not been granted the powers of self-government, ...
. The county was named for the
Arapaho Nation of
Native Americans who lived in the region.
In June 1858,
gold
Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
was discovered along the
South Platte River
The South Platte River is one of the two principal tributaries of the Platte River. Flowing through the U.S. states of Colorado and Nebraska, it is itself a major river of the American Midwestern United States, Midwest and the American Sou ...
in
Arapahoe County (in present-day
Englewood) by
William Greeneberry Russell
William Greeneberry "Green" Russell (1818–1877) was an American gold prospector and miner.
Early life
Green Russell was born in South Carolina but moved with his family to Georgia as a small child. His father James Russell engaged in gold mini ...
and Sam Bates who had been following up the June 22, 1850, discovery of gold on Ralston Creek in today's Jefferson County by Lewis Ralston, for whom the creek was named. This discovery precipitated the
Pike's Peak Gold Rush. The Doniphan Party upon arriving upon Clear Creek discovered markers left over from earlier mining in 1834 by the Estes Party, placed their own alongside and on November 29, 1858, founded the future county's first town of Arapahoe City upon the land southeast of today's West 44th Avenue and McIntyre Street (with West 44th running through the town). On June 16, 1859, its second town,
Golden, Colorado
Golden is a home rule city that is the county seat of Jefferson County, Colorado, United States. The city population was 20,399 at the 2020 United States census. Golden lies along Clear Creek at the base of the Front Range of the Rocky Moun ...
, was founded in the valley to the west. Many residents of the mining region felt disconnected from the remote territorial governments of
Kansas
Kansas ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the west. Kansas is named a ...
and
Nebraska
Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...
, so they voted to form their own
Territory of Jefferson on October 24, 1859. The following month on November 28, 1859, the Jefferson Territorial Legislature organized 12 counties for the new territory, including
Jefferson County. Jefferson County was named for the namesake of the Jefferson Territory,
Thomas Jefferson
Thomas Jefferson (, 1743July 4, 1826) was an American Founding Fathers of the United States, Founding Father and the third president of the United States from 1801 to 1809. He was the primary author of the United States Declaration of Indepe ...
, the principal author of the
Declaration of Independence
A declaration of independence is an assertion by a polity in a defined territory that it is independent and constitutes a state. Such places are usually declared from part or all of the territory of another state or failed state, or are breaka ...
and the nation's third
president
President most commonly refers to:
*President (corporate title)
* President (education), a leader of a college or university
*President (government title)
President may also refer to:
Arts and entertainment Film and television
*'' Præsident ...
.
Golden City was elected on January 2, 1860, as the
county seat
A county seat is an administrative center, seat of government, or capital city of a county or parish (administrative division), civil parish. The term is in use in five countries: Canada, China, Hungary, Romania, and the United States. An equiva ...
of Jefferson County.
Robert Williamson Steele,
Governor
A governor is an politician, administrative leader and head of a polity or Region#Political regions, political region, in some cases, such as governor-general, governors-general, as the head of a state's official representative. Depending on the ...
of the
Provisional Government of the Territory of Jefferson from 1859 to 1861, built his home in the county at
Mount Vernon
Mount Vernon is the former residence and plantation of George Washington, a Founding Father, commander of the Continental Army in the Revolutionary War, and the first president of the United States, and his wife, Martha. An American landmar ...
and later at
Apex
The apex is the highest point of something. The word may also refer to:
Arts and media Fictional entities
* Apex (comics)
A-Bomb
Abomination
Absorbing Man
Abraxas
Abyss
Abyss is the name of two characters appearing in Ameri ...
. Originally Jefferson County's borders extended to the
40th parallel north
Following are circles of latitude between the 35th parallel north and the 40th parallel north:
36th parallel north
The 36th parallel north is a circle of latitude that is 36 degrees north of the Earth's equatorial plane. It crosses Africa, t ...
, the
South Platte River
The South Platte River is one of the two principal tributaries of the Platte River. Flowing through the U.S. states of Colorado and Nebraska, it is itself a major river of the American Midwestern United States, Midwest and the American Sou ...
(excluding the town of Highland) to the east, and to Bear Creek to the south.
The Jefferson Territory never received federal sanction, but during his last week in office,
President
President most commonly refers to:
*President (corporate title)
* President (education), a leader of a college or university
*President (government title)
President may also refer to:
Arts and entertainment Film and television
*'' Præsident ...
James Buchanan
James Buchanan Jr. ( ; April 23, 1791June 1, 1868) was the 15th president of the United States, serving from 1857 to 1861. He also served as the United States Secretary of State, secretary of state from 1845 to 1849 and represented Pennsylvan ...
signed an act which organized the
Territory of Colorado on February 28, 1861.
That November 1, the new
Colorado General Assembly
The Colorado General Assembly is the state legislature of the State of Colorado. It is a bicameral legislature consisting of the Senate and House of Representatives that was created by the 1876 state constitution. Its statutes are codified in ...
organized the 17 original counties of Colorado, including Jefferson County. The reorganized Jefferson County extended to most of its current borders and Golden continued as county seat. In 1908, the southern tip of Jefferson County was transferred to
Park County, reducing Jefferson County to its present length of . Several annexations by the
City & County of Denver and the 2001 consolidation of the
City & County of Broomfield removed the east and extreme northeastern corner of the county, respectively.
Geography

At the
2020 United States census, the county had a total area of , of which is land and (1.3%) is water.
As of April 1, 2020, the mean population center
of the State of Colorado was located in Jefferson County at coordinates
near the (ironically) tiny hamlet of Phillipsburg.
Adjacent counties
Jefferson County is one of the few counties in the United States to border as many as ten counties.
*
Boulder County – north
*
City and County of Broomfield – northeast
*
Adams County – east
*
City and County of Denver
Denver ( ) is a consolidated city and county, the capital and most populous city of the U.S. state of Colorado. It is located in the Western United States, in the South Platte River Valley on the western edge of the High Plains east of ...
– east
*
Arapahoe County – east
*
Douglas County – east
*
Teller County – south
*
Park County – southwest
*
Clear Creek County – west
*
Gilpin County – northwest
Major highways
*
Interstate 70
Interstate 70 (I-70) is a major east–west Interstate Highway in the United States that runs from Interstate 15, I-15 near Cove Fort, Utah, to Interstate 695 (Maryland), I-695 and Maryland Route 570 (MD 570) in Woodlawn, Baltimo ...
*
*
U.S. Highway 6
*
U.S. Highway 40
*
U.S. Highway 285
*
State Highway 8
*
State Highway 58
*
State Highway 72
*
State Highway 74
*
State Highway 75
*
State Highway 93
*
State Highway 121
*
State Highway 391
*
State Highway 470
*
Chatfield Ave
*
44th Ave
Recreational areas
*Alderfer/Three Sisters Park
*Apex Park
*Bear Creek Lake Park
*
Centennial Cone Park
*Clear Creek Canyon Park
*Coal Creek Canyon
*
Crown Hill Park
*Deer Creek Canyon Park
*
Elk Meadow Park
*Evergreen Lake
*Fairmount Trail
*Flying J Ranch Park
*Hildebrand Ranch Park
*
Hiwan Homestead Museum
*Lair o' the Bear Park
*Lewis Meadows Park
*Lookout Mountain Nature Center
*Matthews/Winters Park
*Meyer Ranch Park
*Mount Falcon Park
*Mount Galbraith Park
*Mount Glennon
*
Mount Lindo
*North Table Mountain Park
*Pine Valley Ranch Park
*Ranson/Edwards Homestead Ranch
*Reynolds Park
*Sister City Park
*South Table Mountain Park
*
South Valley Park
*Standley Lake Regional Park
*Van Bibber Park
*Welchester Tree Grant Park
*White Ranch Park
*Windy Saddle Park
*Urban Trails
Demographics
As of the
census
A census (from Latin ''censere'', 'to assess') is the procedure of systematically acquiring, recording, and calculating population information about the members of a given Statistical population, population, usually displayed in the form of stati ...
of 2000, there were 527,056 people, 206,067 households, and 140,537 families residing in the county. The
population density
Population density (in agriculture: Standing stock (disambiguation), standing stock or plant density) is a measurement of population per unit land area. It is mostly applied to humans, but sometimes to other living organisms too. It is a key geog ...
was . There were 212,488 housing units at an average density of . The racial makeup of the county was
:
There were 206,067 households, out of which 33.40% had children under age 18 living with them, 55.10% were
married couples
Marriage, also called matrimony or wedlock, is a culturally and often legally recognised union between people called spouses. It establishes rights and obligations between them, as well as between them and their children (if any), and b ...
living together, 9.10% had a female householder with no husband present, and 31.80% were non-families. 24.50% of all households were made up of individuals, of those 6.30% were someone living alone who was 65 years of age or older. The average household size was 2.52, and the average family size was 3.03 persons.
In the county, the population ages were spread out:
:
For every 100 females there were 99.00 males. For every 100 females age 18 and over, there were 96.80 males.
The median income for a household in the county was $57,339, and the median income for a family was $67,310. Males had a median income of $45,306 versus $32,372 for females. The
per capita income
Per capita income (PCI) or average income measures the average income earned per person in a given area (city, region, country, etc.) in a specified year.
In many countries, per capita income is determined using regular population surveys, such ...
for the county was $28,066. About 3.40% of families and 5.20% of the population were below the
poverty line
The poverty threshold, poverty limit, poverty line, or breadline is the minimum level of income deemed adequate in a particular country. The poverty line is usually calculated by estimating the total cost of one year's worth of necessities for ...
, including 5.80% of those under age 18, and 5.10% of those age 65 or over.
According to a report in the
JAMA
''JAMA'' (''The Journal of the American Medical Association'') is a peer-reviewed medical journal published 48 times a year by the American Medical Association. It publishes original research, reviews, and editorials covering all aspects of b ...
, residents of Jefferson County had a 2014 life expectancy of 80.02 years.
Education
The sole school district serving the county is
Jefferson County School District R-1.
;Private schools:
*
Colorado Academy
Colorado Academy (CA) is an independent nonsectarian, co-educational, college preparatory day school for students from Pre-Kindergarten through Twelfth Grade. The school's campus is located in Lakewood, Colorado, and serves approximately 1000 ...
;Higher Education:
*
Colorado Christian University
Colorado Christian University (CCU) is a private Christian university in Lakewood, Colorado, United States. CCU was founded by Clifton Fowler in 1914 as the Denver Bible Institute.
History
CCU's heritage dates back to the formation of Denver Bi ...
*
Colorado School of Mines
The Colorado School of Mines (Mines) is a public research university in Golden, Colorado, United States. Founded in 1874, the school offers both undergraduate and graduate degrees in engineering, science, and mathematics, with a focus on ener ...
*
Red Rocks Community College
Red Rocks Community College (RRCC) is a Public university, public community college with two campuses located in Lakewood, Colorado, Lakewood and Arvada, Colorado.
History
RRCC was established in 1969 as part of the Colorado Community Colle ...
*
Rocky Mountain College of Art and Design
Jefferson County Public Library is the county library system.
Government and infrastructure
*The
Federal Correctional Institution, Englewood is in
unincorporated Jefferson County.
*The
Rocky Flats Plant produced nuclear weapons in Jefferson County from 1952 until 1989.
*The
Jefferson County Public Library, established in 1952.
*The
Jefferson County Government Center, also known as the "courts and admin building".
*The
Denver Federal Center, the largest concentration of federal government agencies outside of
Washington, D.C.
Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city and federal district of the United States. The city is on the Potomac River, across from Virginia, and shares land borders with ...
, is located in Lakewood.
Government
The Board of County Commissioners operates as the governing body of the county. Established in 1861, the board consists of three commissioners who are elected
at-large
At large (''before a noun'': at-large) is a description for members of a governing body who are elected or appointed to represent a whole membership or population (notably a city, county, state, province, nation, club or association), rather tha ...
to four-year terms. The board sets policies that guide county programs and operations which serves residents and businesses. There are several elected officials that oversee a department or aspect of county operations.
Jefferson County lies within the 1st Judicial District which is represented by District Attorney Alexis King.
Sheriff's office
The Jefferson County Sheriff is an oldest elective office in Jefferson County (along with Clerk and Recorder, Assessor and Treasurer) and among the first popularly elected offices in Colorado, established in 1859 with the first Sheriff, Walter Pollard, elected on January 2, 1860. Its office holders over the course of over 150 years have included some of the most noted law enforcement officers in Colorado history.
The Jefferson County Sheriff's Office responded to the 1999
Columbine High School massacre
A school shooting and attempted bombing occurred on April 20, 1999, at Columbine High School in Columbine, Colorado, United States. The perpetrators, twelfth-grade students Eric Harris and Dylan Klebold, murdered 13 students and one teach ...
, and investigated it together with the
F.B.I. The Sheriff's Office received backlash after it was revealed the agency had the perpetrators
Eric Harris and Dylan Klebold
Eric David Harris (April 9, 1981 – April 20, 1999) and Dylan Bennet Klebold ( ; September 11, 1981 – April 20, 1999) were American high school seniors and mass murderers who perpetrated the Columbine High School massacre at Columbine ...
in and out of custody prior to the shooting. After the shooting
Sue Klebold sued the Sheriff's office for failing to prevent their son from carrying out the Columbine High shootings. According to a "notice of intent to sue" filed by Susan and Thomas Klebold, county officials were "reckless, willful and wanton" in the way they handled a 1998 police report about Eric Harris' Internet ravings.
This lawsuit was dismissed along with several others pertaining to the shooting.
The current county sheriff is Regina "Reggie" Marinelli. She was elected in 2022 and became the first woman to do so in county history and became the first Democrat to hold the office in nearly a century. She previously worked in the county Sheriff's Office for over 30 years.
Politics
Jefferson County was a Republican stronghold for most of the 20th century, voting Republican in all but one presidential election between 1940 and 2004. However, it has voted Democratic in every presidential election since 2008, consistent with the general trend in the Denver metropolitan area. In
2024
The year saw the list of ongoing armed conflicts, continuation of major armed conflicts, including the Russian invasion of Ukraine, the Myanmar civil war (2021–present), Myanmar civil war, the Sudanese civil war (2023–present), Sudane ...
,
Kamala Harris
Kamala Devi Harris ( ; born October 20, 1964) is an American politician and attorney who served as the 49th vice president of the United States from 2021 to 2025 under President Joe Biden. She is the first female, first African American, and ...
won the largest percentage for a Democratic presidential candidate since
1916.
Recreation
State parks
*
Chatfield State Park
*
Golden Gate Canyon State Park
*
Staunton State Park
Staunton State Park is a Colorado state park in Park and Jefferson counties, located west of Conifer, Colorado. The park, which opened on May 18, 2013, includes dramatic rock outcroppings, several streams and a waterfall. On December 4, 201 ...
National forests and wilderness
*
Pike National Forest
*
Roosevelt National Forest
The Roosevelt National Forest is a National Forest located in north central Colorado. It is contiguous with the Colorado State Forest as well as the Arapaho National Forest and the Routt National Forest. The forest is administered jointly w ...
*
Lost Creek Wilderness
National wildlife refuges
*
Rocky Flats National Wildlife Refuge
*
Two Ponds National Wildlife Refuge
Historic trail
*
South Platte Trail
Recreational trails
*
American Discovery Trail
*
Apex National Recreation Trail
*
Big Dry Creek National Recreation Trail
*
Colorado Trail
*
Platte River Greenway National Recreation Trail
*
Two Ponds National Recreation Trail
Scenic byway
*
Lariat Loop Scenic and Historic Byway
Golf course
*
Hiwan Golf Club
*
Indian Tree Golf Club
Communities
Cities
*
Arvada (part)
*
Edgewater
*
Golden
*
Lakewood
*
Littleton (part)
*
Westminster
Westminster is the main settlement of the City of Westminster in Central London, Central London, England. It extends from the River Thames to Oxford Street and has many famous landmarks, including the Palace of Westminster, Buckingham Palace, ...
(part)
*
Wheat Ridge
Towns
*
Bow Mar (part)
*
Lakeside
*
Morrison Morrison may refer to:
People
* Morrison (surname), people with the Scottish surname Morrison
* Morrison Heady (1829–1915), American poet
* Morrison Mann MacBride (1877–1938), Canadian merchant
Places in the United States
* Morrison, Colorad ...
*
Mountain View
*
Superior (part)
Census-designated places
*
Applewood
*
Aspen Park
*
Brook Forest
*
Coal Creek (part)
*
Columbine
*
Dakota Ridge
*
East Pleasant View
*
Evergreen
In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional throughout the year. This contrasts with deciduous plants, which lose their foliage completely during the winter or dry season. Consisting of many diffe ...
*
Fairmount
*
Genesee
*
Idledale
*
Indian Hills
*
Ken Caryl
*
Kittredge
*
West Pleasant View
Unincorporated communities
*
Buffalo Creek
*
Conifer
Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...
*
Foxton
*
Pine
A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae.
''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as cu ...
*
Pine Junction
*
Plastic
Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
See also
*
Bibliography of Colorado
This is a bibliography of the U.S. State of Colorado.
__TOC__
General history
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*
*
*
*
*
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*
*
*
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*
*
*
*
*Sibley, George. ''Water Wranglers - The 75-Year History of the Colorado River District: A Story About the Embattled Co ...
*
Geography of Colorado
The geography of the U.S. State of Colorado is diverse, encompassing rugged mountainous terrain, vast plains, desert lands, desert canyons, and mesas. Colorado is a landlocked U.S. state. In 1861, the United States Congress defined the boun ...
*
History of Colorado
The region that is today the U.S. state of Colorado has been inhabited by Native Americans and their Paleoamerican ancestors for at least 13,500 years and possibly more than 37,000 years. The eastern edge of the Rocky Mountains was a major mi ...
**
Arapahoe County, Kansas Territory
**
*
Index of Colorado-related articles
This is an alphabetical list of articles related to the U.S. State of Colorado.
0–9
* .co.us – Internet second-level domain for the State of Colorado
* 4 Corners
** 4 Corners Monument
* 6th Principal Meridian
* 10-mile Range
* 10 ...
*
List of Colorado-related lists
The following two master lists include links to lists related to the United States, U.S. Colorado, State of Colorado.
#Colorado-related lists by topic
#Alphabetical list of Colorado-related lists
Colorado-related lists by topic General lists
*Bib ...
**
List of counties in Colorado
The U.S. State of Colorado is divided into 64 counties. Two of these, the City and County of Denver, which serves as the state capital, and the City and County of Broomfield, have consolidated city and county governments. In addition to Denv ...
**
List of statistical areas in Colorado
The United States, U.S. Colorado, State of Colorado has 20 Statistical area (United States), statistical areas that have been delineated by the Office of Management and Budget (OMB). Statistical areas are important geographic delineations of pop ...
*
Outline of Colorado
The following Outline (list), outline is provided as an overview of and topical guide to the U.S. state of Colorado:
Colorado – List of U.S. states and territories by population#State and territory rankings, 22nd most populous, the Lis ...
**
Front Range Urban Corridor
References
External links
Jefferson County Government websiteColorado Historical Society
{{coord, 39.59, -105.25, display=title, type:adm2nd_region:US-CO_source:UScensus1990
Colorado counties
1861 establishments in Colorado Territory
Denver metropolitan area
Populated places established in 1861