| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Potsdam | 1 | 14,188 | 14,949 | -1.25% | 140 | 101 | Town |
| Massena | 2 | 11,958 | 12,421 | -0.83% | 270 | 44 | Town |
| Canton | 3 | 11,132 | 11,669 | -1.1% | 106 | 105 | Town |
| Massena | 4 | 9,830 | 10,253 | -0.69% | 2,170 | 5 | Village |
| Ogdensburg | 5 | 8,970 | 9,872 | -1.68% | 1,810 | 5 | City |
| Potsdam | 6 | 7,941 | 8,493 | -0.97% | 1,615 | 5 | Village |
| Canton | 7 | 6,833 | 7,252 | -0.88% | 1,648 | 4 | Village |
| Gouverneur | 8 | 6,368 | 6,503 | -0.72% | 89 | 71 | Town |
| Norfolk | 9 | 4,282 | 4,448 | -0.72% | 75 | 57 | Town |
| Lisbon | 10 | 4,265 | 4,205 | 0.16% | 39 | 108 | Town |
| Oswegatchie | 11 | 3,979 | 4,144 | 0.08% | 61 | 65 | Town |
| Stockholm | 12 | 3,850 | 3,817 | -0.18% | 41 | 94 | Town |
| Gouverneur | 13 | 3,548 | 3,625 | -0.34% | 1,619 | 2 | Village |
| Louisville | 14 | 2,958 | 3,046 | -0.54% | 61 | 49 | Town |
| Brasher | 15 | 2,587 | 2,607 | 0.66% | 28 | 91 | Town |
| Pierrepont | 16 | 2,524 | 2,507 | -0.04% | 42 | 60 | Town |
| De Kalb | 17 | 2,332 | 2,369 | -0.17% | 28 | 83 | Town |
| Waddington | 18 | 2,217 | 2,219 | -0.14% | 43 | 52 | Town |
| Fowler | 19 | 2,149 | 2,132 | 0.09% | 36 | 59 | Town |
| Morristown | 20 | 2,052 | 2,076 | -0.29% | 45 | 46 | Town |
| Parishville | 21 | 1,989 | 2,022 | -0.05% | 20 | 98 | Town |
| Russell | 22 | 1,850 | 1,863 | -0.16% | 19 | 97 | Town |
| Madrid | 23 | 1,706 | 1,746 | -0.41% | 32 | 53 | Town |
| Norwood | 24 | 1,510 | 1,572 | -0.72% | 721 | 2 | Village |
| Colton | 25 | 1,475 | 1,522 | -0.54% | 6.0 | 242 | Town |
| Fine | 26 | 1,254 | 1,298 | -0.71% | 8.0 | 167 | Town |
| Hammond | 27 | 1,241 | 1,258 | -0.32% | 20 | 62 | Town |
| Hermon | 28 | 1,096 | 1,071 | 0.18% | 21 | 53 | Town |
| Hopkinton | 29 | 1,067 | 1,106 | -0.74% | 6.0 | 185 | Town |
| De Peyster | 30 | 1,049 | 1,019 | -0.29% | 24 | 43 | Town |
| Edwards | 31 | 978 | 1,010 | -0.61% | 20 | 50 | Town |
| Macomb | 32 | 928 | 917 | -0.43% | 15 | 61 | Town |
| Waddington | 33 | 924 | 924 | -0.11% | 424 | 2 | Village |
| Pitcairn | 34 | 810 | 791 | 1% | 14 | 59 | Town |
| Rossie | 35 | 765 | 795 | -0.91% | 20 | 38 | Town |
| Heuvelton | 36 | 704 | 717 | -0.28% | 925 | 1 | Village |
| Clifton | 37 | 666 | 676 | -0.45% | 5.0 | 134 | Town |
| Rensselaer Falls | 38 | 318 | 318 | 0% | 1,093 | 0 | Village |
| Hammond | 39 | 280 | 285 | -0.36% | 478 | 1 | Village |
| Piercefield | 40 | 270 | 283 | -0.74% | 3.0 | 104 | Town |
| Richville | 41 | 255 | 266 | -0.78% | 346 | 1 | Village |
| Clare | 42 | 91 | 94 | 0% | 1.0 | 96 | Town |
Potsdam is the largest city in St. Lawrence County, with a population of 14,188.
Clare is the smallest city in St. Lawrence County, with a population of 91.
There are 42 cities in St. Lawrence County, New York.