Idaho Counties by Population (2025)

There are 44 counties in Idaho.

Ada County is the largest county in the state, with a population of 544,908. The most recent census shows that its population has increased by 0.09% since the previous census.

A number of other Idaho counties also boast relatively large populations for their state, though not able to match the density of Ada County:

• Canyon County : 275,042
• Kootenai County : 191,409

Idaho Counties with the Fewest Residents

The smallest county in Idaho is Clark County , with a population of just 787. This total represents a decrease of 0.0% since the last census count was performed.

Other small counties include:

• Camas County : 1,262
• Butte County : 2,723
• Lewis County : 3,716

Idaho Counties with Rapid Growth

Boundary County , with its current population of 14,403, has shown the largest population growth, with an increase of 0.2% since the last census.

Ada County has also had relatively high population growth of 0.09% with 544,908 residents.

On the other hand, Clark County has had the largest decrease in population, with its 787 current residents totalling 0.0% less than the previous census.