Population of Counties in Idaho (2020)

As of 2019, Idaho's most populous county is Ada County, home of Boise, with 469,966 residents. This represents a population growth of 19.48% since the 2010 census. Ada County is followed by Canyon County (223,499), Kootenai County (161,505), and Bonneville County (116,854). These are the only counties in Idaho with a population exceeding 100,000. Of these counties, Ada County experienced the highest population growth.

Idaho Counties with Fewest Residents

The least populated county in Idaho is Clark County with a population of 852 in 2019, down 13.06% since the last census. There are 15 counties in Idaho with fewer than 10,000 residents. Other small counties in Idaho are Camas County (1,127), Butte County (2,611), Lewis County (3,861), Adams County (4,250), Custer County (4,280), and Oneida County (4,488). Of these counties, Clark County experienced the most dramatic decline with a population growth rate of -13.06%. Adams County experienced the highest growth with a population that grew by 7.27% since the census.

Idaho Counties with Rapid Growth

Ada County, the largest county in Idaho, also experienced the most rapid growth over the last decade, climbing 19.48% to 469,966 people. Other cities that have experienced rapid growth include Canyon County (18.03%), Kootenai County (16.31%), Teton County (14.67%), Valley County (12.80%), and Jefferson County (12.27%). Only 8 counties in Idaho experienced negative growth since the census. The most dramatic decline was in Clark County, which dropped 13.06%, followed by Butte County at -10.43%. No other county experienced decline of more than 2%.

Name 2020 Population Growth Since 2010
Ada County469,96619.48%
Canyon County223,49918.03%
Kootenai County161,50516.31%
Bonneville County116,85411.64%
Bannock County87,1384.96%
Twin Falls County86,08111.02%
Bingham County46,2361.02%
Bonner County44,7279.34%
Nez Perce County40,4082.78%
Latah County40,1347.73%
Madison County39,3044.55%
Jefferson County29,43912.27%
Elmore County27,2590.51%
Jerome County24,0156.95%
Cassia County23,8643.40%
Payette County23,5514.04%
Blaine County22,6016.13%
Minidoka County20,8253.69%
Gem County17,6345.68%
Idaho County16,5131.25%
Gooding County15,196-1.78%
Franklin County13,7267.39%
Fremont County13,168-0.42%
Shoshone County12,7960.20%
Boundary County11,9488.63%
Owyhee County11,6931.92%
Teton County11,64014.67%
Valley County11,04112.80%
Washington County10,161-0.16%
Benewah County9,226-0.69%
Clearwater County8,7580.36%
Lemhi County7,9610.11%
Power County7,768-1.32%
Boise County7,6348.96%
Caribou County7,0601.23%
Bear Lake County6,0501.36%
Lincoln County5,3602.96%
Oneida County4,4884.66%
Custer County4,280-1.77%
Adams County4,2507.27%
Lewis County3,8611.07%
Butte County2,611-10.43%
Camas County1,1270.99%
Clark County852-13.06%