New Hampshire Counties by Population (2025)

There are 10 counties in New Hampshire.

The most populous county in New Hampshire is Hillsborough County, which is home to 415,427 residents. This is about 30.61% of the state’s total population. Since 2010, Hillsborough County has grown 3.54%.

The second-most populous county in New Hampshire is Rockingham County with a population of 309,176 people, about 22.79% of the population, followed by Merrimack County with 151,132 people, about 11.14% of the state population. Both Rockingham and Merrimack have grown since the 2010 Census by 4.70% and 3.24%, respectively.

Counties with Fewest Residents

Of New Hampshire‘s 10 counties, Coos County has the fewest residents at 31,589. This is about 2.33% of the state’s total population. The population density is 17.60 persons per square mile.

The second-least populated county in New Hampshire is Sullivan County, which is home to 43,144 people, about 3.18% of the state’s total population. This is followed by Carroll County with a population of 48,799 people.

Counties with Rapid Growth

Seven out of the 10 New Hampshire counties have experienced growth since the 2010 Census. Strafford County experienced the highest population growth of 5.60%, followed by Rockingham County with 4.70% and Hillsborough County with 3.54%.

The three counties that experienced a population decline since 2010 are:

• Coos County (4.20%)
• Sullivan County (1.41%)
• Cheshire County (0.73%)