Map of Idaho Counties

Idaho has 44 counties, and the Ultimaps map of Idaho includes all 44. No county has been created in Idaho since 1919, when Caribou, Clark and Jerome counties were formed. Owyhee County is the oldest, created in 1863, the year Idaho Territory was established. Of the 44, 28 were formed after Idaho became the 43rd state on July 3, 1890, and 21 of those date from 1911 to 1919. County populations range from 535,799 in Ada County to 794 in Clark County, according to the US Census Bureau's 2024 estimates. Each county has one county seat, such as Boise for Ada County and Dubois for Clark County.

Idaho County is the largest county in Idaho by area, with 8,477.5 square miles (21,957 km²) of land according to the US Census Bureau's Gazetteer Files (2026). It is larger than several US states. The county seat is Grangeville. The county also includes Riggins, access to Hells Canyon and large parts of the Frank Church-River of No Return Wilderness. Owyhee County, in the state's southwest corner, ranks second with 7,668.2 square miles (19,861 km²), and Custer County is third with 4,922.2 square miles (12,748 km²). At the other end, Payette County has the least land, 406.9 square miles (1,054 km²), under 5% of Idaho County's total.

Ada County is the most populated county in Idaho, with 535,799 residents in the US Census Bureau's estimates for July 1, 2024. It contains Boise, the state capital and largest city, as well as Meridian. Ada grew from 498,301 in 2020, a gain of 37,498 and the largest of any Idaho county. Canyon County, west of Ada, ranks second with 266,892 residents in Nampa, Caldwell and the surrounding area. Ada and Canyon counties are home to about 40% of Idaho's 2,001,619 residents. Kootenai County, home to Coeur d'Alene, is third with 188,323, and Bonneville County, with Idaho Falls, is fourth with 133,644.

Clark County is the least populous county in Idaho, with 794 residents in the US Census Bureau's 2024 estimates, one more than its 2020 figure of 793. Its county seat is Dubois. Clark County lies in eastern Idaho on the Montana border and has 1,763.1 square miles (4,566 km²) of land (Census Gazetteer Files, 2026), or about 0.45 residents per square mile. It was created in 1919, which makes it one of Idaho's three newest counties. The next least populous are Camas County (seat: Fairfield), with 1,247 residents, and Butte County (seat: Arco), with 2,735. Ada County, the most populous, had 535,799.

Boise is not in Boise County. Idaho's capital and largest city is the county seat of Ada County, which had 535,799 residents in the US Census Bureau's 2024 estimates, the most of any Idaho county. Boise County borders Ada County to the northeast and has its seat at Idaho City. It had 8,581 residents in 2024 and covers 1,899.4 square miles (4,919 km²) of land (Census Gazetteer Files, 2026). That gives Ada County more than 60 times as many people. Both counties were created in 1864. Ada County is named for Ada Riggs, the daughter of H.C. Riggs, one of Boise's founders.

Nine northern Idaho counties are on Pacific Time: Benewah, Bonner, Boundary, Clearwater, Kootenai, Latah, Lewis, Nez Perce and Shoshone. Idaho County is split between the two zones. Its northern part, including Grangeville, uses Pacific Time, and its southern part uses Mountain Time. The rest of the state, including Boise, Idaho Falls, Pocatello and Twin Falls, is on Mountain Time, one hour ahead of Pacific Time. Kootenai County, home to Coeur d'Alene, is the most populous Pacific Time county, with 188,323 residents in the US Census Bureau's 2024 estimates. Coeur d'Alene, Moscow and Lewiston share a time zone with Spokane and Seattle, not with Boise.

Idaho's newest counties, Caribou, Clark and Jerome, were all created in 1919. No county has been added since, so the state still has 44. Caribou County (seat: Soda Springs) had 7,239 residents in the US Census Bureau's 2024 estimates. Jerome County (seat: Jerome) had 26,056, and Clark County (seat: Dubois) had 794. The three were the last of 21 counties created between 1911 and 1919. That group also includes Bonneville (1911), Madison (1913), Teton (1915) and Valley (1917). Owyhee County is the oldest county and dates to 1863, the year Idaho Territory was established.

Owyhee County takes its name from Owyhee, an older English spelling of Hawaii. The name honors Hawaiian fur trappers, then called Owyhees, who disappeared in the region. Owyhee County lies in the southwest corner of Idaho, bordering Oregon and Nevada. It is the oldest county on the current list, created in 1863. With 7,668.2 square miles (19,861 km²) of land (Census Gazetteer Files, 2026), it is the second largest county after Idaho County. It had 12,748 residents in the US Census Bureau's 2024 estimates, fewer than two per square mile. The county seat is Murphy, and the county includes the Owyhee Canyonlands and the desert around Bruneau.

You can build a custom map of Idaho in the Ultimaps editor. It is free, and no sign-up is required. If your data is in a spreadsheet, import a file that lists county names with a value for each. The editor colors every matched county on a scale you choose and adds a legend. To highlight only a few counties, such as Ada and Canyon, click each one and pick a color. Pins mark point locations, like a branch in Pocatello or a job site near Salmon. You can also change the palette, borders, labels and title. Free exports are standard PNG files with a small Ultimaps credit. To export high-resolution PNG, SVG or PDF files, you need Pro.