What are the largest counties in New Hampshire?

Hillsborough County is the largest county in New Hampshire, with 433,415 residents in 2025 (Census PEP). Rockingham County (324,077) and Merrimack County (158,078) come next.

Data as of 2025 · updated November 5, 2026

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All 10 ranked New Hampshire counties

New Hampshire counties ranked by population
Rank	County	Residents 2025	Change 2020–25
1	Hillsborough County	433,415	+2.5%
2	Rockingham County	324,077	+3.0%
3	Merrimack County	158,078	+2.6%
4	Strafford County	135,043	+3.0%
5	Grafton County	93,225	+2.2%
6	Cheshire County	78,269	+2.3%
7	Belknap County	65,147	+2.1%
8	Carroll County	52,784	+5.0%
9	Sullivan County	43,961	+2.1%
10	Coos County	31,343	+0.3%

How this is ranked

The Census Bureau's July 1 resident population estimates for 2025, largest first, with the change since 2020. Counties with fewer than 1,000 residents are not ranked. Areas without an estimate for the same year as the others are not ranked.

Source: U.S. Census Bureau, Population Estimates Program (Vintage 2025). Figures come from public federal statistics and are informational only, not investment advice. Check the source before relying on a number. Methodology: how ranks and figures are built.

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Questions

What is the largest county in New Hampshire?

Hillsborough County is the largest county in New Hampshire, with 433,415 residents in 2025 (Census PEP). Rockingham County (324,077) and Merrimack County (158,078) come next.

How is this ranking calculated?

More rankings for New Hampshire

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