| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Thompson | 1 | 16,631 | 16,550 | -0.54% | 198 | 84 | Town |
| Fallsburg | 2 | 15,206 | 14,062 | 0.33% | 196 | 78 | Town |
| Mamakating | 3 | 12,586 | 12,661 | -0.91% | 131 | 96 | Town |
| Liberty | 4 | 10,288 | 10,155 | -0.75% | 129 | 80 | Town |
| Monticello | 5 | 7,198 | 7,236 | 0.04% | 1,764 | 4 | Village |
| Liberty | 6 | 5,132 | 5,018 | 0.69% | 1,958 | 3 | Village |
| Bethel | 7 | 4,368 | 3,953 | 1.68% | 51 | 85 | Town |
| Neversink | 8 | 3,354 | 3,371 | -0.86% | 41 | 83 | Town |
| Rockland | 9 | 3,317 | 3,270 | -0.54% | 35 | 94 | Town |
| Callicoon | 10 | 3,043 | 2,991 | -0.52% | 63 | 49 | Town |
| Lumberland | 11 | 2,300 | 2,240 | -0.26% | 49 | 47 | Town |
| Delaware | 12 | 2,199 | 2,198 | -0.54% | 63 | 35 | Town |
| Cochecton | 13 | 1,421 | 1,446 | -0.98% | 39 | 36 | Town |
| Tusten | 14 | 1,419 | 1,407 | -1.18% | 30 | 47 | Town |
| Fremont | 15 | 1,133 | 1,159 | -1.22% | 23 | 50 | Town |
| Wurtsboro | 16 | 1,081 | 1,091 | 0% | 865 | 1 | Village |
| Bloomingburg | 17 | 977 | 993 | -0.1% | 1,420 | 1 | Village |
| Forestburgh | 18 | 813 | 806 | -0.73% | 15 | 55 | Town |
| Woodridge | 19 | 737 | 710 | 0.14% | 440 | 2 | Village |
| Jeffersonville | 20 | 390 | 391 | 0.26% | 956 | 0 | Village |
Thompson is the largest city in Sullivan County, with a population of 16,631.
Jeffersonville is the smallest city in Sullivan County, with a population of 390.
There are 20 cities in Sullivan County, New York.