Ada County, Idaho

Ada County
County
James A. McClure Federal Building and U.S. Courthouse in Boise, Idaho.
Seal
Location within the U.S. state of Idaho
Idaho's location within the U.S.
Coordinates: 43°27′N 116°14′W / 43.45°N 116.24°W / 43.45; -116.24
Country	United States
State	Idaho
Founded	December 22, 1864
Named for	Ada Riggs
Seat	Boise
Largest city	Boise
Area
• Total	1,060 sq mi (2,700 km2)
• Land	1,053 sq mi (2,730 km2)
• Water	7.9 sq mi (20 km2)  0.7%
Population  (2020)
• Total	494,967
• Estimate  (2022)	518,907
• Density	470/sq mi (180/km2)
Time zone	UTC−7 (Mountain)
• Summer (DST)	UTC−6 (MDT)
Congressional districts	1st, 2nd
Website	www.adaweb.net
County Code: 1A

Ada County is located in the southwestern part of Idaho, United States. As of the 2020 census, the county had a population of 494,967,^[1] which by 2022 was estimated to have risen to 518,907.^[2] Ada County is by far the state's most populous county; it is home to 26.8% of the state's population. The county seat and largest city is Boise,^[3] which is also the state capital.^[4] Ada County is included in the Boise metropolitan area. The Ada County Highway District has jurisdiction over all the local county and city streets, except for private roads and state roads. In the interior Pacific Northwest east of the Cascade Range, Ada County ranks second in population, behind Spokane County, Washington.