Ada County, Idaho
Ada County, Idaho | |
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James A. McClure Federal Building and U.S. Courthouse in Boise, Idaho | |
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Seal | |
Location within the U.S. state of Idaho | |
| Coordinates: 43°27′N 116°14′W / 43.45°N 116.24°W | |
| Country | United States |
| State | Idaho |
| Founded | December 22, 1864 |
| Named after | Ada Riggs |
| Seat | Boise |
| Largest city | Boise |
| Area | |
• Total | 1,060 sq mi (2,745 km2) |
| • Land | 1,052 sq mi (2,725 km2) |
| • Water | 7.7 sq mi (20 km2) 0.7% |
| Population (2020) | |
• Total | 494,967 |
• Estimate (2024) | 535,799 |
| • Density | 470.4/sq mi (181.6/km2) |
| Time zone | UTC−7 (Mountain) |
| • Summer (DST) | UTC−6 (MDT) |
| Congressional districts | 1st, 2nd |
| Website | adacounty |
| 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, which by 2024 was estimated to have risen to 535,799. 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, which is also the state capital. 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.