Ada County is located in the

southwestern The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each sepa ...

part of

Idaho Idaho ( ) is a state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and Wyom ...

, United States. As of the 2021 United States census estimate, the

county A county is a geographic region of a country used for administrative or other purposesChambers Dictionary, L. Brookes (ed.), 2005, Chambers Harrap Publishers Ltd, Edinburgh in certain modern nations. The term is derived from the Old French ...

had a population of 511,931, making it by far the state's most populous county; it is home to 26.8% of the state's population. The

county seat A county seat is an administrative center, seat of government, or capital city of a county or civil parish. The term is in use in Canada, China, Hungary, Romania, Taiwan, and the United States. The equivalent term shire town is used in the US st ...

and largest city is

Boise Boise (, , ) is the capital and most populous city of the U.S. state of Idaho and is the county seat of Ada County. On the Boise River in southwestern Idaho, it is east of the Oregon border and north of the Nevada border. The downtown area' ...

, which is also the state capital. Ada County is included in the Boise metropolitan area. The

Ada County Highway District The Ada County Highway District (ACHD) is the only countywide highway district in Idaho. Located in Garden City, Idaho, it is a government agency established in 1971 as an independent government entity. Overview ACHD covers the entirety of Ada ...

has jurisdiction over all the local county and city streets, except for private roads and state roads. In the interior

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Tho ...

east of the

Cascade Range The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...

, Ada County ranks second in population, behind

Spokane County, Washington Spokane County is a county located in the U.S. state of Washington. As of the 2020 census, its population was 539,339, making it the fourth-most populous county in Washington. The largest city and county seat is Spokane, the second largest cit ...

History

Ada County was created by the Idaho Territory legislature on December 22, 1864, partitioned from Boise County. It is named for Ada Riggs, the daughter of H.C. Riggs, a member of the legislature; he established the county and was a co-founder of

. Canyon County, which originally included Payette County and most of Gem County, was partitioned from western Ada County in 1891.

Geography

According to the

U.S. Census Bureau The United States Census Bureau (USCB), officially the Bureau of the Census, is a principal agency of the U.S. Federal Statistical System, responsible for producing data about the American people and economy. The Census Bureau is part of the ...

, the county has a total area of , of which is land and (0.7%) is water. The Boise River flows through the northern portion of the county, and the northwest border is bounded by the foothills of the Boise Range mountains; the summits are in adjacent Boise County. The southwestern border of the county is bounded by the

Snake River The Snake River is a major river of the greater Pacific Northwest region in the United States. At long, it is the largest tributary of the Columbia River, in turn, the largest North American river that empties into the Pacific Ocean. The Snake ...

Adjacent counties

* Gem County - northwest * Boise County - northeast * Elmore County - east *

Owyhee County Owyhee County ( ) is a county in the southwestern corner of the U.S. state of Idaho. As of the 2020 census, the population was 12,133. The county seat is Murphy, and its largest city is Homedale. In area it is the second-largest county in Ida ...

- south * Canyon County - west

Major highways

* - Interstate 84 * -

Interstate 184 Interstate 184 (I-184) is a short auxiliary Interstate Highway in Boise, Idaho, United States. It is a spur route of I-84 that connects the freeway to Downtown Boise, terminating at US Highway 20 (US 20) and US 26. Route ...

* -

US 20 U.S. Route 20 or U.S. Highway 20 (US 20) is an east–west United States Numbered Highway that stretches from the Pacific Northwest east to New England. The "0" in its route number indicates that US 20 is a major coast-to-coast route. S ...

* -

US 26 U.S. Route 26 (US 26) is an east–west United States highway that runs from Seaside, Oregon to Ogallala, Nebraska. When the U.S. highway system was first defined, it was limited to Nebraska and Wyoming; by the 1950s, it continued into Idaho and ...

* -

US 30 U.S. Route 30 or U.S. Highway 30 (US 30) is an east–west main route in the system of the United States Numbered Highways, with the highway traveling across the northern tier of the country. With a length of , it is the third longest ...

* - SH-16 * - SH-21 - ''Ponderosa Pine Scenic Byway'' * - SH-44 * - SH-55 - ''Payette River Scenic Byway'' * -

SH-69 Route 69, or Highway 69, may refer to: International * European route E69 Australia * Appin Road Canada * Alberta Highway 69 * Ontario Highway 69 China * G69 Expressway Finland * Finnish national road 69 India * National Highway 69 (I ...

County roads and highways are maintained by the

National protected areas

Boise National Forest Boise National Forest is a National Forest covering of the U.S. state of Idaho. Created on July 1, 1908, from part of Sawtooth National Forest, it is managed by the U.S. Forest Service as five units: the Cascade, Emmett, Idaho City, Low ...

(part) *

Snake River Birds of Prey National Conservation Area The Morley Nelson Snake River Birds of Prey National Conservation Area has one of the densest populations of nesting raptors. The National Conservation Area (NCA) is located south of Boise, Idaho along of the Snake River, and is managed by the B ...

(part)

Demographics

2000 census

As of the

2000 United States census The United States census of 2000, conducted by the Census Bureau, determined the resident population of the United States on April 1, 2000, to be 281,421,906, an increase of 13.2 percent over the 248,709,873 people enumerated during the 1990 ce ...

, there were 300,904 people, 113,408 households, and 77,344 families in the county. The

population density Population density (in agriculture: 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 geographical term.Matt RosenberPopul ...

was 285/mi² (110/km²). There were 118,516 housing units at an average density of 112/mi² (43/km²). The

racial makeup A race is a categorization of humans based on shared physical or social qualities into groups generally viewed as distinct within a given society. The term came into common usage during the 1500s, when it was used to refer to groups of variou ...

of the county was 92.86% White, 0.65% Black or African American, 0.69% Native American, 1.74% Asian, 0.15% Pacific Islander, 1.67% from other races, and 2.24% from two or more races. Hispanic or Latino of any race were 4.48% of the population. There were 113,408 households, out of which 36.20% had children under the age of 18 living with them, 55.10% were married couples living together, 9.40% had a female householder with no husband present, and 31.80% were non-families. 23.80% of all households were made up of individuals, and 6.07% had someone living alone who was 65 years of age or older. The average household size was 2.59 and the average family size was 3.11. The county population contained 27.30% under the age of 18, 10.30% from 18 to 24, 32.50% from 25 to 44, 20.80% from 45 to 64, and 9.10% who were 65 years of age or older. The median age was 33 years. For every 100 females, there were 100.6 males. For every 100 females age 18 and over, there were 98.9 males. The median income for a household in the county was $46,140, and the median income for a family was $54,416. Males had a median income of $37,867 versus $26,453 for females. The

per capita income Per capita income (PCI) or total income measures the average income earned per person in a given area (city, region, country, etc.) in a specified year. It is calculated by dividing the area's total income by its total population. Per capita i ...

for the county was $22,519. About 5.40% of families and 7.70% 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 t ...

, including 9.20% of those under age 18 and 5.70% of those age 65 or over.

2010 census

As of the

2010 United States census The United States census of 2010 was the twenty-third United States national census. National Census Day, the reference day used for the census, was April 1, 2010. The census was taken via mail-in citizen self-reporting, with enumerators servin ...

, there were 392,365 people, 148,445 households, and 99,282 families in the county. The population density was . There were 159,471 housing units at an average density of . The

of the county was 90.3% white, 2.4% Asian, 1.1% black or African American, 0.7% American Indian, 0.2% Pacific islander, 2.4% from other races, and 2.8% from two or more races. Those of Hispanic or Latino origin made up 7.1% of the population. In terms of ancestry, 19.4% were

German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...

, 15.9% were

English English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ide ...

, 11.8% were

Irish Irish may refer to: Common meanings * Someone or something of, from, or related to: ** Ireland, an island situated off the north-western coast of continental Europe ***Éire, Irish language name for the isle ** Northern Ireland, a constituent unit ...

, and 8.6% were

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

. Of the 148,445 households, 35.6% had children under the age of 18 living with them, 52.4% were married couples living together, 10.0% had a female householder with no husband present, 33.1% were non-families, and 25.0% of all households were made up of individuals. The average household size was 2.58 and the average family size was 3.11. The median age was 34.8 years. The median income for a household in the county was $55,835 and the median income for a family was $67,519. Males had a median income of $48,290 versus $34,875 for females. The per capita income for the county was $27,915. About 6.9% of families and 10.2% of the population were below the poverty line, including 11.8% of those under age 18 and 6.8% of those age 65 or over.

Government and politics

Ada County has traditionally been rather conservative for an urban county. Like Idaho as a whole, it has long been a Republican Party stronghold. The last victory in a presidential election by a

Democrat Democrat, Democrats, or Democratic may refer to: Politics *A proponent of democracy, or democratic government; a form of government involving rule by the people. *A member of a Democratic Party: **Democratic Party (United States) (D) **Democratic ...

in Ada County was by

Franklin D. Roosevelt Franklin Delano Roosevelt (; ; January 30, 1882April 12, 1945), often referred to by his initials FDR, was an American politician and attorney who served as the 32nd president of the United States from 1933 until his death in 1945. As the ...

in 1936. It rejected

Lyndon B. Johnson Lyndon Baines Johnson (; August 27, 1908January 22, 1973), often referred to by his initials LBJ, was an American politician who served as the 36th president of the United States from 1963 to 1969. He had previously served as the 37th vice ...

in 1964 during his 44-state landslide. In 2008 the presidential election in Ada County was more competitive than in previous years;

John McCain John Sidney McCain III (August 29, 1936 – August 25, 2018) was an American politician and United States Navy officer who served as a United States senator from Arizona from 1987 until his death in 2018. He previously served two terms ...

defeated

Barack Obama Barack Hussein Obama II ( ; born August 4, 1961) is an American politician who served as the 44th president of the United States from 2009 to 2017. A member of the Democratic Party, Obama was the first African-American president of the U ...

by six percentage points. Obama became the first Democrat to garner as much as 40 percent of the county's vote since Lyndon B. Johnson. In 2016,

Donald Trump Donald John Trump (born June 14, 1946) is an American politician, media personality, and businessman who served as the 45th president of the United States from 2017 to 2021. Trump graduated from the Wharton School of the University of Pe ...

won the county by only a plurality due to high third party performance. In 2020, whereas the state of Idaho trended very strongly for Trump, he carried Ada County by a slim majority, only beating Joe Biden by around 4 percentage points. This is the narrowest election in decades for Ada County, and the closest a Democrat has come to carrying the county since 1940. Democratic

gubernatorial A governor is an administrative leader and head of a polity or political region, ranking under the head of state and in some cases, such as governors-general, as the head of state's official representative. Depending on the type of political ...

nominee Jerry Brady carried the county in his 2002 and

2006 File:2006 Events Collage V1.png, From top left, clockwise: The 2006 Winter Olympics open in Turin; Twitter is founded and launched by Jack Dorsey; The Nintendo Wii is released; Montenegro 2006 Montenegrin independence referendum, votes to declare ...

races, despite losing statewide in both contests. Another prominent Democrat, Boise mayor David Bieter, was elected in 2007, 2011 and 2015. Ada County is split between the

first First or 1st is the ordinal form of the number one (#1). First or 1st may also refer to: *World record, specifically the first instance of a particular achievement Arts and media Music * 1$T, American rapper, singer-songwriter, DJ, and rec ...

and

second The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ...

congressional districts; it is the only county in the state that is not located entirely within one district. As of 2022, the first district is represented by

Russ Fulcher Russell Mark Fulcher (born March 9, 1962) is an American businessman and politician serving as the U.S. representative for Idaho's 1st congressional district since 2019. A member of the Republican Party, he represented the 21st district in the ...

and includes

Meridian Meridian or a meridian line (from Latin ''meridies'' via Old French ''meridiane'', meaning “midday”) may refer to Science * Meridian (astronomy), imaginary circle in a plane perpendicular to the planes of the celestial equator and horizon * ...

Eagle Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, some of which are closely related. Most of the 68 species of eagle are from Eurasia and Africa. Outside this area, j ...

and

Kuna Kuna may refer to: Places * Kuna, Idaho, a town in the United States ** Kuna Caves, a lava tube in Idaho * Kuna Peak, a mountain in California * , a village in the Orebić municipality, Croatia * , a village in the Konavle municipality, Croatia ...

, while the second district is represented by

Mike Simpson Michael Keith Simpson (born September 8, 1950) is an American politician and former dentist serving as the U.S. representative for since 1999. The district covers most of the eastern portion of the state, including Idaho Falls, Pocatello, S ...

and includes most of Boise proper. Both Fulcher and Simpson are Republicans. In the

Idaho Legislature The Idaho Legislature consists of the upper Idaho Senate and the lower Idaho House of Representatives. Idaho is divided into 35 legislative districts, which each elect one senator and two representatives. There are no term limits for either ...

, Ada County is split among nine districts, the most of any county. Each district elects one state senator and two state representatives. As of 2022, In the state senate, Republicans hold five seats and Democrats hold four. In the state house, Republicans hold ten seats and Democrats hold eight. Generally, Democratic strength is concentrated in Boise itself, while Republican strength is concentrated in the western suburbs. Several of the Boise seats were Democratic pickups in 2006. Each party held all of their respective legislative seats in the 2008 elections, but Republicans won two competitive county commission races.

County offices

The county government is administered by the Ada County Board of Commissioners, a three-member legislative body. Other elected officials include

clerk A clerk is a white-collar worker who conducts general office tasks, or a worker who performs similar sales-related tasks in a retail environment. The responsibilities of clerical workers commonly include record keeping, filing, staffing service ...

, treasurer,

sheriff A sheriff is a government official, with varying duties, existing in some countries with historical ties to England where the office originated. There is an analogous, although independently developed, office in Iceland that is commonly transla ...

, assessor, coroner, and

prosecutor A prosecutor is a legal representative of the prosecution in states with either the common law adversarial system or the Civil law (legal system), civil law inquisitorial system. The prosecution is the legal party responsible for presenting the ...

. The

Idaho Department of Correction The Idaho Department of Correction (IDOC) operates nine prisons, four community release centers and 20 probation and parole offices in seven districts located throughout the state of Idaho. The agency has its headquarters in Boise. IDOC employs a ...

operates the South Boise Prison Complex, a correctional facility located in

unincorporated Unincorporated may refer to: * Unincorporated area, land not governed by a local municipality * Unincorporated entity, a type of organization * Unincorporated territories of the United States, territories under U.S. jurisdiction, to which Congress ...

Ada County, south of the

Boise Airport Boise Airport (Boise Air Terminal or Gowen Field) is a joint civil-military airport in the western United States, south of downtown Boise in Ada County, Idaho. The airport is operated by the city of Boise Department of Aviation and is oversee ...

and east of Kuna.

Education

Public school districts

School districts include: *

Boise School District The Boise School District #1 is one of 115 public school districts in Idaho. The Boise School District serves a 456 square mile area of Ada County and is headquartered in Boise, Idaho. The district was founded in 1865 under the auspices of Idaho ...

* Kuna Joint School District 3 * Melba Joint School District 136 *

West Ada School District The West Ada School District #2, long known as the Meridian School District, is a school district based in Meridian, Idaho. In addition to Meridian, the district operates public schools in Eagle, Star and western Boise. It is the largest school ...

(Meridian Joint School District 2)

Communities

Cities

* Garden City *

Star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

Census-designated places

* Avimor *

Hidden Springs Hidden Springs is a populated place situated in Coconino County, Arizona, United States, located on U.S. 89 approximately 75 miles north of Flagstaff. It has an estimated elevation of above sea level. The San Juan Southern Paiute Tribe of Arizo ...

Unincorporated communities

* Mora * Pleasant Valley * Sonna

Population ranking

The population ranking of the following table is based on the 2010 census of Ada County. † ''county seat''

References

External links

* {{authority control Idaho counties 1864 establishments in Idaho Territory Boise metropolitan area Populated places established in 1864