Sullivan County area

Population and density of Sullivan County

The Census Bureau estimates that 43,961 people lived in Sullivan County on July 1, 2025. That ranks #1,139 of 3,222 county equivalents nationally and #9 of 10 in New Hampshire. Since the April 1, 2020 estimates base of 43,065, the population has grown by 896 (+2.1%), compared with +2.7% for New Hampshire as a whole.

With 537.9 square miles of land, that is 82 people per square mile (32 per km²), placing Sullivan County #1,139 nationally for density and #7 in New Hampshire. The median county equivalent has 47 people per square mile; the New Hampshire median is 136. Put another way, there are about 7.8 acres of land per resident.

U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.

Cities and towns in Sullivan County

Sullivan County is divided into 15 cities and towns. In New Hampshire, county subdivisions are local governments, and together they cover all of the county’s land and residents; a few are unorganized areas without their own government.

The most populous is Claremont city, with 13,032 residents (29.6% of the county). The largest by land is Plainfield town, at 52.2 mi², or 9.7% of the county’s land. The county seat, Newport town, has 6,417 residents. Among those with at least 1,000 residents in 2020, Springfield town grew fastest since then (+5%).

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each subdivision inside Sullivan County. Land: 2026 Census Gazetteer. How communities are listed.

Metropolitan area

Sullivan County is an outlying county of the Lebanon-Claremont, NH-VT Micropolitan Statistical Area. Its 4 county equivalents have 224,500 residents on 3,902.6 square miles of land; Sullivan County accounts for 13.8% of the land and 19.6% of the residents. By combined land it ranks #38 of 542 micropolitan areas, and #2 by population.

ZIP codes

19 ZIP Code Tabulation Areas have land in Sullivan County; 15 of them have most of their land inside the county, and the others mainly cover neighboring areas.

03244032570328003284036010360203603036050360703743037450374803751037520375303770037730378103782

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering Sullivan County

Sullivan County shares a land border with 6 county equivalents, including 2 in Vermont. Each of them has more land than Sullivan County. The largest neighbor is Grafton County (1,708.6 mi²) and the smallest is Cheshire County (706.7 mi²). Together with its neighbors, Sullivan County forms a block of 6,517.7 mi² of land, of which it holds 8.3%.

How big is Sullivan County compared with U.S. states?

Sullivan County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.9 times as much. New Hampshire’s county land could hold about 17 areas the size of Sullivan County.

Another way to picture it: the same land area would fill a square about 23.2 miles (37.3 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.

State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.

What stands out about Sullivan County?

Sullivan County has more land than 1,278 of the other 3,221 county equivalents in the dataset.

A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.

Does including water change its rank?

Using land plus water places Sullivan County at #2,001 nationally by total area, 57 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.

Its water share is 2.6%, compared with a national county-equivalent median of 1.2% — 1.4 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.

Closest positions in the national land ranking

These entries sit immediately beside Sullivan County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.