Ada County, Idaho

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Ada County, Idaho
Seal of Ada County, Idaho
Map of Idaho highlighting Ada County
Location in the state of Idaho
Map of the United States highlighting Idaho
Idaho's location in the U.S.
Founded December 22, 1864
Named for Ada Riggs, first pioneer child born in county
Seat Boise
Largest city Boise
 • Total 1,060 sq mi (2,745 km2)
 • Land 1,053 sq mi (2,727 km2)
 • Water 7.9 sq mi (20 km2), 0.7%
 • (2010) 392,365
 • Density 373/sq mi (144/km²)
Congressional districts 1st, 2nd
Time zone Mountain: UTC-7/-6

Ada County is a county in the southwestern part of the U.S. state of Idaho. As of the 2010 Census, the county had a population of 392,365,[1] making it the most populous county in Idaho. The county seat and largest city is Boise,[2] which is also the state capital.[3]

Ada County is included in the Boise, ID Metropolitan Statistical Area.

Ada County is by far the state's largest in population, containing more than one quarter of the state's residents, and contains its only county highway district; the Ada County Highway District (ACHD) has jurisdiction over all the local county and city streets, except for private roads and state roads. In the interior Northwest east of the Cascade Range, Ada County ranks second in population behind only Spokane County, Washington.


Ada County was created by the Idaho Territorial Legislature on December 22, 1864, partitioned from Boise County. It is named for Ada Riggs, the first pioneer child born in the area and the daughter of H.C. Riggs, a co-founder of Boise.[4] Canyon County, which originally included Payette County and most of Gem County, was partitioned from western Ada County in 1891.


According to the U.S. Census Bureau, the county has a total area of 1,060 square miles (2,700 km2), of which 1,053 square miles (2,730 km2) is land and 7.9 square miles (20 km2) (0.7%) is water.[5] 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.

Adjacent counties[edit]

Major highways[edit]

County roads and highways are maintained by the Ada County Highway District (ACHD).

National protected areas[edit]


Historical population
Census Pop.
1870 2,675
1880 4,674 74.7%
1890 8,368 79.0%
1900 11,559 38.1%
1910 29,088 151.6%
1920 35,213 21.1%
1930 37,925 7.7%
1940 50,401 32.9%
1950 70,649 40.2%
1960 93,460 32.3%
1970 112,230 20.1%
1980 173,036 54.2%
1990 205,775 18.9%
2000 300,904 46.2%
2010 392,365 30.4%
Est. 2014 426,236 [6] 8.6%
U.S. Decennial Census[7]
1790-1960[8] 1900-1990[9]
1990-2000[10] 2010-2013[1]

As of the census[11] of 2000, there were 300,904 people, 113,408 households, and 77,344 families residing in the county. The population density was 285/mi² (110/km²). There were 118,516 housing units at an average density of 112/mi² (43/km²). The racial makeup 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.

In the county the population was spread out with 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 for the county was $22,519. About 5.40% of families and 7.70% of the population were below the poverty line, including 9.20% of those under age 18 and 5.70% of those age 65 or over.

Government and politics[edit]

Similar to other Idaho counties, an elected three-member county commission heads the county government. Other elected officials include clerk, treasurer, sheriff, assessor, coroner, and prosecutor.[12]

Ada County has traditionally been a Republican Party stronghold. The last victory in a presidential election by a Democrat in Ada County was by Franklin D. Roosevelt in 1936 - the last time a Democrat carried the state of Idaho was Lyndon B. Johnson in 1964.[13] In 2008 the presidential election in Ada County was more competitive than in previous years; John McCain defeated Barack Obama by six percentage points.[14]

Democratic gubernatorial nominee Jerry Brady carried the county in his 2002 and 2006 races, despite losing statewide in both contests.[15][16] Another prominent Democrat, Boise mayor David H. Bieter, was comfortably reelected in nonpartisan races in 2007 and 2011.[17]

In the Idaho Legislature, Ada County is split between nine districts, the most of any county.[18] In the state house, Republicans hold ten seats and Democrats hold eight. In the state senate, Republicans hold five seats and Democrats hold four. Generally, Democratic strength is concentrated in Boise itself, while Republican strength is concentrated in the western suburbs.[19] Several of the Boise seats were Democratic pickups in 2006.[20]

Each party held all of their respective legislative seats the 2008 elections, but Republicans won two competitive county commission races.[21]

The Idaho Department of Correction operates the South Boise Prison Complex,[22] is a correctional facility located in unincorporated Ada County, south of the Boise Airport and east of Kuna.[23]


Public school districts[edit]



Census-designated place[edit]

See also[edit]


  1. ^ a b "State & County QuickFacts". United States Census Bureau. Retrieved June 28, 2014. 
  2. ^ "Find a County". National Association of Counties. Retrieved 2011-06-07. 
  3. ^ Idaho Department of Commerce (2011). "Facts About Idaho". Idaho Department of Commerce. Retrieved 2011-11-10. 
  4. ^ "Ada County". Retrieved 7 January 2015. 
  5. ^ "US Gazetteer files: 2010, 2000, and 1990". United States Census Bureau. 2011-02-12. Retrieved 2011-04-23. 
  6. ^ "Annual Estimates of the Resident Population for Incorporated Places: April 1, 2010 to July 1, 2014". Retrieved June 4, 2015. 
  7. ^ "U.S. Decennial Census". United States Census Bureau. Retrieved June 28, 2014. 
  8. ^ "Historical Census Browser". University of Virginia Library. Retrieved June 28, 2014. 
  9. ^ "Population of Counties by Decennial Census: 1900 to 1990". United States Census Bureau. Retrieved June 28, 2014. 
  10. ^ "Census 2000 PHC-T-4. Ranking Tables for Counties: 1990 and 2000" (PDF). United States Census Bureau. Retrieved June 28, 2014. 
  11. ^ "American FactFinder". United States Census Bureau. Retrieved 2008-01-31. 
  12. ^ Ada County Portal
  13. ^ 1964 Presidential General Election Results - Idaho
  14. ^ 2008 - General Election Ada County
  15. ^ November 5, 2002 General Election Results
  16. ^ November 7, 2006 General Election Results
  17. ^ Bieter beats Tibbs in Boise mayor race
  18. ^ Idaho Legislative District Map
  19. ^ Idaho Legislative Districts
  20. ^ Baseline 08: Idaho Legislature
  21. ^ Election shows GOP still has the edge in Ada County
  22. ^ "Information Technology Projects." Idaho Department of Correction. March 2011. Retrieved on June 3, 2011.
  23. ^ "Locations." Idaho Department of Correction. Retrieved on June 4, 2011. Kuna area addresses: "South Idaho Correctional Institution Community Work Center (CWC) 14195 S. Pleasant Valley Road Kuna ID 83634" "Correctional Alternative Placement Program (CAPP) 15505 S. Pleasant Valley Rd. Kuna ID 83634" "Idaho Correctional Center (ICC) 14601 S. Pleasant Valley Rd Kuna ID 83634" "Idaho Maximum Security Institution (IMSI) 13400 S. Pleasant Valley Rd Kuna ID 83634" "Idaho State Correctional Institution (ISCI) 13500 S. Pleasant Valley Rd Kuna ID 83634" "South Boise Women's Correctional Center (SBWCC) 13200 S. Pleasant Valley Rd. Kuna ID 83634" "South Idaho Correctional Institution (SICI) 13900 S. Pleasant Valley Rd Kuna ID 83634"

Further reading[edit]

External links[edit]

Coordinates: 43°27′N 116°14′W / 43.45°N 116.24°W / 43.45; -116.24