New Hampshire Counties by Population (2025)

There are 10 counties in New Hampshire.

Hillsborough County is the largest county in the state, with a population of 433,205. The most recent census shows that its population has increased by 0.02% since the previous census.

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

• Rockingham County : 324,201
• Merrimack County : 158,679

New Hampshire Counties with the Fewest Residents

The smallest county in New Hampshire is Coos County , with a population of just 30,979. This total represents a decrease of 0.0% since the last census count was performed.

Other small counties include:

• Sullivan County : 44,018
• Carroll County : 52,787
• Belknap County : 65,495

New Hampshire Counties with Rapid Growth

Carroll County , with its current population of 52,787, has shown the largest population growth, with an increase of 0.1% since the last census.

On the other hand, Coos County has had the largest decrease in population, with its 30,979 current residents totalling 0.0% less than the previous census.