15 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Claremont | 1 | 13,057 | 12,953 | -0.18% | 303 | 43 | City |
| Newport | 2 | 6,434 | 6,300 | 0.12% | 148 | 44 | Town |
| Charlestown | 3 | 4,897 | 4,801 | -0.22% | 137 | 36 | Town |
| Grantham | 4 | 3,485 | 3,409 | 0.03% | 128 | 27 | Town |
| Sunapee | 5 | 3,471 | 3,351 | 0.17% | 165 | 21 | Town |
| Plainfield | 6 | 2,562 | 2,460 | 0.23% | 49 | 52 | Town |
| Cornish | 7 | 1,644 | 1,616 | -0.12% | 39 | 42 | Town |
| Unity | 8 | 1,507 | 1,509 | -0.46% | 41 | 37 | Town |
| Springfield | 9 | 1,326 | 1,250 | 0.38% | 30 | 44 | Town |
| Washington | 10 | 1,229 | 1,193 | 0.66% | 27 | 46 | Town |
| Lempster | 11 | 1,174 | 1,114 | 0.69% | 36 | 32 | Town |
| Acworth | 12 | 900 | 860 | 0.45% | 23 | 39 | Town |
| Croydon | 13 | 874 | 805 | 1.04% | 24 | 37 | Town |
| Goshen | 14 | 804 | 798 | -0.37% | 36 | 22 | Town |
| Langdon | 15 | 660 | 650 | -0.3% | 41 | 16 | Town |
Claremont is the largest city in Sullivan County, with a population of 13,057.
Langdon is the smallest city in Sullivan County, with a population of 660.
There are 15 cities in Sullivan County, New Hampshire.