Ada County, Idaho
The most populous of Idaho's 44 counties.
CountyFIPS 16001
- Population
- 546,141
- +47,878 (+9.6%) since 2020
- Land area
- 1,052
- square miles. A further 0.8% of the total area is water
- Population density
- 519
- people per square mile, computed rather than published
- County seat
- Boise
- Seat of county government.
- Established
- 1864
- 161 years ago
- Largest city
- Boise City city
- Population 238,429.
Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.
Satellite view
Aerial imagery of Ada County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.
Where Ada County ranks
Position among the 44 counties of Idaho, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.
| Measure | Value | In Idaho | Nationally |
|---|---|---|---|
| Population | 546,141 | 1st of 44 | 134th of 3,144 |
| Land area | 1,052 sq mi | 31st of 44 | 620th of 3,144 |
| Population density | 519 per sq mi | 1st of 44 | 275th of 3,144 |
| Median household income | $91,502 | 3rd of 44 | 276th of 3,143 |
Full data for Ada County
| Measure | Value | Source and vintage |
|---|---|---|
| Population | 546,141 | Vintage 2025 Population Estimates |
| Population in 2020 | 498,263 | Vintage 2025 Population Estimates |
| 2020 estimates base? | 494,966 | Vintage 2025 Population Estimates |
| Land area | 1,052 sq mi | 2025 Gazetteer Files |
| Water area | 8.5 sq mi | 2025 Gazetteer Files |
| Total area | 1,061 sq mi | 2025 Gazetteer Files |
| Population density? | 519 per sq mi | Computed: Vintage 2025 estimates divided by 2025 Gazetteer land area |
| Median household income | $91,502 | American Community Survey 2020-2024 5-Year Estimates |
| Median home value | $512,300 | American Community Survey 2020-2024 5-Year Estimates |
| Median age | 38.4 | American Community Survey 2020-2024 5-Year Estimates |
| Households | 202,543 | American Community Survey 2020-2024 5-Year Estimates |
| Housing units | 211,440 | American Community Survey 2020-2024 5-Year Estimates |
Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.
How the population changed
The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:
- Births minus deaths
- +1,629
- 5,549 births, 3,920 deaths
- Net migration
- +9,307
- More people moved in than moved out.
Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.
The 5 areas bordering Ada County
Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.
| Bordering area | State | Shared border | Population |
|---|---|---|---|
| Elmore County | Idaho | 48 mi | 29,465 |
| Canyon County | Idaho | 40 mi | 275,123 |
| Owyhee County | Idaho | 22 mi | 12,661 |
| Boise County | Idaho | 22 mi | 8,545 |
| Gem County | Idaho | 12 mi | 21,773 |
Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.
All 44 counties of Idaho
Open the interactive Idaho county map, or jump straight to any of them.
- Ada County
- Adams County
- Bannock County
- Bear Lake County
- Benewah County
- Bingham County
- Blaine County
- Boise County
- Bonner County
- Bonneville County
- Boundary County
- Butte County
- Camas County
- Canyon County
- Caribou County
- Cassia County
- Clark County
- Clearwater County
- Custer County
- Elmore County
- Franklin County
- Fremont County
- Gem County
- Gooding County
- Idaho County
- Jefferson County
- Jerome County
- Kootenai County
- Latah County
- Lemhi County
- Lewis County
- Lincoln County
- Madison County
- Minidoka County
- Nez Perce County
- Oneida County
- Owyhee County
- Payette County
- Power County
- Shoshone County
- Teton County
- Twin Falls County
- Valley County
- Washington County
Data on this page last rebuilt 30 August 2026. How these figures are produced.