55 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Potsdam town | 1 | 14,758 | 14,909 | -0.2% | 146 | 101.38 | Town |
| Massena town | 2 | 12,130 | 12,406 | -0.56% | 274 | 44.34 | Town |
| Canton town | 3 | 11,259 | 11,794 | -0.82% | 108 | 104.73 | Town |
| Massena | 4 | 9,973 | 10,245 | -0.54% | 2,202 | 4.53 | Village |
| Ogdensburg | 5 | 8,928 | 9,867 | -2.06% | 1,801 | 4.96 | City |
| Potsdam | 6 | 8,406 | 8,481 | -0.18% | 1,709 | 4.92 | Village |
| Canton | 7 | 6,852 | 7,381 | -1.52% | 1,653 | 4.14 | Village |
| Gouverneur town | 8 | 6,610 | 6,485 | 0.75% | 93 | 71.20 | Town |
| Norfolk town | 9 | 4,347 | 4,460 | -0.48% | 77 | 56.74 | Town |
| Lisbon town | 10 | 4,289 | 4,219 | 0.37% | 40 | 108.28 | Town |
| Oswegatchie town | 11 | 3,995 | 4,148 | 0.2% | 61 | 65.50 | Town |
| Stockholm town | 12 | 3,864 | 3,819 | 0.29% | 41 | 93.90 | Town |
| Gouverneur | 13 | 3,616 | 3,618 | 0% | 1,650 | 2.19 | Village |
| Louisville town | 14 | 2,991 | 3,046 | -0.23% | 62 | 48.52 | Town |
| Brasher town | 15 | 2,545 | 2,620 | -0.55% | 28 | 91.11 | Town |
| Pierrepont town | 16 | 2,539 | 2,518 | 0.2% | 42 | 60.23 | Town |
| De Kalb town | 17 | 2,333 | 2,369 | -0.21% | 28 | 82.52 | Town |
| Waddington town | 18 | 2,249 | 2,235 | 0.22% | 44 | 51.61 | Town |
| Fowler town | 19 | 2,136 | 2,135 | -0.28% | 36 | 59.18 | Town |
| Morristown town | 20 | 2,068 | 2,079 | -0.1% | 45 | 45.73 | Town |
| Parishville town | 21 | 1,999 | 2,037 | -0.4% | 20 | 98.11 | Town |
| Russell town | 22 | 1,873 | 1,873 | -0.16% | 19 | 96.50 | Town |
| Madrid town | 23 | 1,706 | 1,736 | -0.41% | 32 | 52.98 | Town |
| Norwood | 24 | 1,530 | 1,565 | -0.46% | 730 | 2.10 | Village |
| Colton town | 25 | 1,499 | 1,531 | -0.4% | 6 | 241.70 | Town |
| Fine town | 26 | 1,278 | 1,306 | -0.47% | 8 | 166.61 | Town |
| Hammond town | 27 | 1,250 | 1,258 | -0.24% | 20 | 62.21 | Town |
| Hermon town | 28 | 1,103 | 1,074 | 0.46% | 21 | 53.15 | Town |
| Hopkinton town | 29 | 1,075 | 1,102 | -0.56% | 6 | 185.34 | Town |
| De Peyster town | 30 | 1,070 | 1,017 | 0.85% | 25 | 42.93 | Town |
| Edwards town | 31 | 998 | 1,012 | -0.2% | 20 | 50.14 | Town |
| Macomb town | 32 | 968 | 918 | 1.04% | 16 | 60.72 | Town |
| Waddington | 33 | 941 | 938 | 0.11% | 432 | 2.18 | Village |
| Hannawa Falls | 34 | 854 | 1,040 | -1.5% | 167 | 5.13 | CDP |
| Madrid | 35 | 838 | 805 | 0.6% | 225 | 3.73 | CDP |
| Pitcairn town | 36 | 796 | 791 | 0.13% | 14 | 58.80 | Town |
| Rossie town | 37 | 775 | 795 | -0.51% | 21 | 37.79 | Town |
| Norfolk | 38 | 755 | 886 | -4.79% | 279 | 2.70 | CDP |
| Heuvelton | 39 | 720 | 719 | 0% | 946 | 0.76 | Village |
| Clifton town | 40 | 677 | 678 | -0.15% | 5 | 134.35 | Town |
| DeKalb Junction | 41 | 676 | 535 | 1.5% | 170 | 3.98 | CDP |
| Edwards | 42 | 675 | 430 | 7.14% | 730 | 0.93 | CDP |
| Parishville | 43 | 647 | 623 | 0% | 196 | 3.29 | CDP |
| Hailesboro | 44 | 628 | 776 | 0% | 134 | 4.70 | CDP |
| Star Lake | 45 | 609 | 540 | -2.09% | 140 | 4.34 | CDP |
| Hermon | 46 | 596 | 387 | 7.19% | 1,211 | 0.49 | CDP |
| Brasher Falls | 47 | 470 | 605 | -2.89% | 286 | 1.64 | CDP |
| Rensselaer Falls | 48 | 321 | 323 | 0% | 1,103 | 0.29 | Village |
| Hammond | 49 | 283 | 285 | 0% | 483 | 0.59 | Village |
| Piercefield town | 50 | 275 | 282 | -0.36% | 3 | 104.16 | Town |
| Richville | 51 | 258 | 267 | -0.77% | 350 | 0.74 | Village |
| Colton | 52 | 256 | 290 | -2.29% | 154 | 1.66 | CDP |
| Winthrop | 53 | 166 | 174 | -12.17% | 60 | 2.78 | CDP |
| Cranberry Lake | 54 | 105 | 126 | -5.41% | 5 | 19.42 | CDP |
| Clare town | 55 | 89 | 93 | -1.11% | 1 | 96.50 | Town |
Potsdam town is the largest city in St. Lawrence County, with a population of 14,758.
Clare town is the smallest city in St. Lawrence County.
There are 55 cities in St. Lawrence County, New York.