Idaho Counties by Population (2025)

There are 44 counties in Idaho.

Ada County, home of Boise, is Idaho’s most populous county with 469,966 residents. This represents a population growth of 19.48% since the 2010 census.

Other large counties in Idaho include:

• Canyon County: 223,499 (growth rate of 18.03%)
• Kootenai County: 161,505 (growth rate of 16.31%)
• Bonneville County: 116,854

These are the only counties in Idaho with a population exceeding 100,000. Of these, 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, down -13.06% since the last census.

There are 15 counties in Idaho with fewer than 10,000 residents. Other small counties include:

• Camas County: 1,127
• Butte County: 2,611
• Lewis County: 3,861
• Adams County: 4,250 (growth rate of 7.27%)
• Custer County: 4,280
• Oneida County: 4,488

Of these counties, Clark County experienced the most dramatic decline with a population growth rate of -13.06%.

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 counties with rapid growth include:

• Canyon County: 18.03%
• Kootenai County: 16.31%
• Teton County: 14.67%
• Valley County: 12.80%
• 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 a decline of more than 2%.