19 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Claremont | 1 | 13,218 | 12,950 | 0.41% | 306 | 43.15 | City |
| Claremont city | 2 | 13,041 | 12,950 | -0.27% | 302 | 43.15 | City |
| Newport town | 3 | 6,452 | 6,303 | 0.33% | 148 | 43.57 | Town |
| Newport | 4 | 5,343 | 5,530 | 0.74% | 379 | 14.11 | CDP |
| Charlestown town | 5 | 5,009 | 4,804 | 0.7% | 140 | 35.76 | Town |
| Grantham town | 6 | 3,484 | 3,406 | 0.09% | 128 | 27.22 | Town |
| Sunapee town | 7 | 3,468 | 3,347 | 0.32% | 165 | 21.05 | Town |
| Plainfield town | 8 | 2,548 | 2,462 | 0.12% | 49 | 52.25 | Town |
| Cornish town | 9 | 1,643 | 1,614 | -0.12% | 39 | 41.95 | Town |
| Unity town | 10 | 1,505 | 1,508 | -0.27% | 41 | 36.98 | Town |
| Springfield town | 11 | 1,335 | 1,256 | 0.68% | 31 | 43.61 | Town |
| Washington town | 12 | 1,195 | 1,193 | -0.42% | 26 | 45.71 | Town |
| Lempster town | 13 | 1,155 | 1,116 | 0.09% | 36 | 32.34 | Town |
| Acworth town | 14 | 889 | 859 | 0.11% | 23 | 38.80 | Town |
| Charlestown | 15 | 880 | 933 | -2% | 923 | 0.95 | CDP |
| Croydon town | 16 | 862 | 805 | 1.06% | 23 | 36.77 | Town |
| Goshen town | 17 | 809 | 797 | -0.12% | 36 | 22.44 | Town |
| Langdon town | 18 | 676 | 648 | 0.75% | 42 | 16.25 | Town |
| Plainfield | 19 | 173 | 265 | -1.14% | 299 | 0.58 | CDP |
Claremont is the largest city in Sullivan County, with a population of 13,218.
Plainfield is the smallest city in Sullivan County.
There are 19 cities in Sullivan County, New Hampshire.