| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Le Ray | 1 | 24,050 | 25,497 | -0.86% | 327 | 74 | Town |
| Watertown | 2 | 23,341 | 24,558 | -0.75% | 2,584 | 9 | City |
| Brownville | 3 | 5,639 | 5,829 | -1.04% | 96 | 59 | Town |
| Wilna | 4 | 5,433 | 5,695 | -1.07% | 70 | 78 | Town |
| Watertown | 5 | 5,312 | 5,812 | -0.97% | 149 | 36 | Town |
| Adams | 6 | 4,776 | 4,958 | -1.04% | 113 | 42 | Town |
| Clayton | 7 | 4,476 | 4,739 | -1.39% | 54 | 83 | Town |
| Champion | 8 | 4,392 | 4,549 | -0.99% | 100 | 44 | Town |
| Alexandria | 9 | 3,595 | 3,726 | -1.02% | 50 | 73 | Town |
| Ellisburg | 10 | 3,229 | 3,338 | -0.98% | 38 | 85 | Town |
| Pamelia | 11 | 3,206 | 3,335 | -0.99% | 94 | 34 | Town |
| Carthage | 12 | 3,173 | 3,318 | -0.72% | 1,308 | 2 | Village |
| Hounsfield | 13 | 3,142 | 3,261 | -1.01% | 64 | 49 | Town |
| Rutland | 14 | 2,924 | 3,018 | -0.95% | 65 | 45 | Town |
| Orleans | 15 | 2,694 | 2,785 | -0.99% | 38 | 71 | Town |
| Theresa | 16 | 2,544 | 2,636 | -1.09% | 39 | 65 | Town |
| Cape Vincent | 17 | 2,357 | 2,671 | -3.36% | 42 | 56 | Town |
| Lyme | 18 | 2,175 | 2,289 | -1.09% | 39 | 56 | Town |
| Philadelphia | 19 | 1,932 | 1,965 | -0.26% | 51 | 38 | Town |
| West Carthage | 20 | 1,714 | 1,767 | -0.41% | 1,310 | 1 | Village |
| Clayton | 21 | 1,642 | 1,734 | -0.85% | 1,025 | 2 | Village |
| Adams | 22 | 1,628 | 1,684 | -0.49% | 1,127 | 1 | Village |
| Antwerp | 23 | 1,624 | 1,680 | -1.04% | 15 | 106 | Town |
| Henderson | 24 | 1,386 | 1,436 | -1% | 34 | 41 | Town |
| Sackets Harbor | 25 | 1,331 | 1,374 | -0.45% | 577 | 2 | Village |
| Black River | 26 | 1,199 | 1,261 | -0.75% | 673 | 2 | Village |
| Rodman | 27 | 1,140 | 1,179 | -0.96% | 27 | 42 | Town |
| Philadelphia | 28 | 1,116 | 1,176 | -0.8% | 1,165 | 1 | Village |
| Dexter | 29 | 987 | 1,009 | -0.2% | 1,482 | 1 | Village |
| Alexandria Bay | 30 | 917 | 948 | -0.54% | 1,224 | 1 | Village |
| Brownville | 31 | 907 | 937 | -0.44% | 1,454 | 1 | Village |
| Lorraine | 32 | 888 | 918 | -0.89% | 23 | 39 | Town |
| Theresa | 33 | 721 | 760 | -0.83% | 571 | 1 | Village |
| Cape Vincent | 34 | 710 | 732 | -0.42% | 1,010 | 1 | Village |
| Evans Mills | 35 | 600 | 626 | -0.66% | 734 | 1 | Village |
| Chaumont | 36 | 576 | 608 | -0.86% | 586 | 1 | Village |
| Antwerp | 37 | 501 | 517 | -0.4% | 500 | 1 | Village |
| Glen Park | 38 | 434 | 446 | -0.46% | 608 | 1 | Village |
| Mannsville | 39 | 316 | 326 | -0.63% | 352 | 1 | Village |
| Deferiet | 40 | 246 | 255 | -0.4% | 364 | 1 | Village |
| Ellisburg | 41 | 206 | 214 | -0.48% | 206 | 1 | Village |
| Worth | 42 | 194 | 201 | -1.02% | 4.0 | 43 | Town |
Le Ray is the largest city in Jefferson County, with a population of 24,050.
Worth is the smallest city in Jefferson County, with a population of 194.
There are 42 cities in Jefferson County, New York.