42 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Le Ray | 1 | 24,140 | 25,501 | -0.28% | 328 | 74 | Town |
| Watertown | 2 | 23,780 | 24,553 | -0.54% | 2,633 | 9 | City |
| Brownville | 3 | 5,744 | 5,815 | -0.21% | 97 | 59 | Town |
| Wilna | 4 | 5,554 | 5,697 | -0.39% | 71 | 78 | Town |
| Watertown | 5 | 5,442 | 5,827 | -0.2% | 152 | 36 | Town |
| Adams | 6 | 4,857 | 4,945 | -0.37% | 115 | 42 | Town |
| Clayton | 7 | 4,569 | 4,729 | -0.67% | 55 | 83 | Town |
| Champion | 8 | 4,461 | 4,542 | -0.4% | 101 | 44 | Town |
| Alexandria | 9 | 3,657 | 3,722 | -0.38% | 50 | 73 | Town |
| Ellisburg | 10 | 3,289 | 3,342 | -0.33% | 39 | 85 | Town |
| Pamelia | 11 | 3,250 | 3,328 | -0.37% | 95 | 34 | Town |
| Carthage | 12 | 3,227 | 3,317 | -0.46% | 1,331 | 2 | Village |
| Hounsfield | 13 | 3,215 | 3,263 | -0.34% | 66 | 49 | Town |
| Rutland | 14 | 2,958 | 3,020 | -0.4% | 65 | 45 | Town |
| Orleans | 15 | 2,750 | 2,783 | -0.25% | 39 | 71 | Town |
| Theresa | 16 | 2,604 | 2,641 | -0.34% | 40 | 65 | Town |
| Cape Vincent | 17 | 2,559 | 2,684 | 0.35% | 45 | 56 | Town |
| Lyme | 18 | 2,204 | 2,288 | -0.72% | 39 | 56 | Town |
| Philadelphia | 19 | 1,956 | 1,968 | 0.1% | 52 | 38 | Town |
| West Carthage | 20 | 1,740 | 1,767 | -0.23% | 1,330 | 1 | Village |
| Clayton | 21 | 1,668 | 1,731 | -0.6% | 1,041 | 2 | Village |
| Adams | 22 | 1,663 | 1,687 | -0.24% | 1,151 | 1 | Village |
| Antwerp | 23 | 1,655 | 1,678 | -0.3% | 16 | 106 | Town |
| Henderson | 24 | 1,414 | 1,436 | -0.35% | 34 | 41 | Town |
| Sackets Harbor | 25 | 1,358 | 1,376 | -0.22% | 589 | 2 | Village |
| Black River | 26 | 1,223 | 1,261 | -0.49% | 687 | 2 | Village |
| Rodman | 27 | 1,175 | 1,192 | -0.25% | 28 | 42 | Town |
| Philadelphia | 28 | 1,128 | 1,172 | -0.62% | 1,177 | 1 | Village |
| Dexter | 29 | 1,012 | 1,009 | 0.1% | 1,520 | 1 | Village |
| Alexandria Bay | 30 | 936 | 953 | -0.32% | 1,250 | 1 | Village |
| Brownville | 31 | 923 | 937 | -0.22% | 1,479 | 1 | Village |
| Lorraine | 32 | 896 | 917 | -0.44% | 23 | 39 | Town |
| Theresa | 33 | 733 | 760 | -0.54% | 580 | 1 | Village |
| Cape Vincent | 34 | 722 | 736 | -0.28% | 1,027 | 1 | Village |
| Evans Mills | 35 | 608 | 623 | -0.33% | 744 | 1 | Village |
| Chaumont | 36 | 587 | 610 | -0.68% | 597 | 1 | Village |
| Antwerp | 37 | 509 | 517 | -0.2% | 507 | 1 | Village |
| Glen Park | 38 | 444 | 447 | 0% | 622 | 1 | Village |
| Mannsville | 39 | 318 | 324 | -0.31% | 355 | 1 | Village |
| Deferiet | 40 | 255 | 258 | 0% | 378 | 1 | Village |
| Ellisburg | 41 | 209 | 214 | -0.48% | 209 | 1 | Village |
| Worth | 42 | 199 | 200 | 0% | 5 | 43 | Town |
Le Ray is the largest city in Jefferson County, with a population of 24,140.
Worth is the smallest city in Jefferson County, with a population of 199.
There are 42 cities in Jefferson County, New York.