Ada County
Sign in to savecounty in Idaho, United States
Key facts
- Country
- United States
- State
- Idaho
- Founded
- December 22, 1864
- Named after
- Ada Riggs
- Seat
- Boise
- Largest city
- Boise
- Total
- 1,060 sq mi (2,745 km )
- Land
- 1,052 sq mi (2,725 km )
- Water
- 7.7 sq mi (20 km ) 0.7%
- Estimate 2025
- 546,141
- Density
- 470.4/sq mi (181.6/km )
- Time zone
- UTC−7 ( Mountain )
- Summer dst
- UTC−6 ( MDT )
- Congressional districts
- 1st , 2nd
- Website
- adacounty .id .gov
via Wikipedia infobox
Article
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 2025 was estimated to have risen to 546,141. 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.
History