33 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Port Huron | 1 | 28,045 | 28,935 | -0.52% | 3,461 | 8 | City |
| Fort Gratiot charter | 2 | 12,035 | 11,229 | 1.44% | 754 | 16 | Township |
| Port Huron charter | 3 | 10,639 | 10,789 | -0.14% | 829 | 13 | Township |
| Marysville | 4 | 9,802 | 9,999 | -0.34% | 1,338 | 7 | City |
| Kimball | 5 | 9,627 | 9,620 | 0.01% | 259 | 37 | Township |
| Clay | 6 | 8,223 | 8,447 | -0.33% | 232 | 35 | Township |
| St. Clair | 7 | 7,146 | 7,098 | 0.11% | 186 | 38 | Township |
| St. Clair | 8 | 6,002 | 5,468 | 1.51% | 2,041 | 3 | City |
| Clyde | 9 | 5,403 | 5,517 | -0.26% | 152 | 36 | Township |
| Ira | 10 | 5,140 | 4,988 | 0.55% | 302 | 17 | Township |
| Casco | 11 | 4,447 | 4,018 | 1.37% | 121 | 37 | Township |
| Columbus | 12 | 4,325 | 4,126 | 0.68% | 118 | 37 | Township |
| Mussey | 13 | 4,153 | 4,239 | -0.26% | 116 | 36 | Township |
| Algonac | 14 | 4,070 | 4,192 | -0.49% | 2,868 | 1 | City |
| Burtchville | 15 | 4,035 | 4,073 | -0.05% | 260 | 16 | Township |
| Marine City | 16 | 3,973 | 4,072 | -0.4% | 1,843 | 2 | City |
| East China | 17 | 3,659 | 3,704 | 0% | 555 | 7 | Township |
| Cottrellville | 18 | 3,530 | 3,412 | 1.32% | 169 | 21 | Township |
| China | 19 | 3,485 | 3,503 | -0.23% | 102 | 34 | Township |
| Riley | 20 | 3,174 | 3,198 | -0.22% | 83 | 38 | Township |
| Wales | 21 | 3,157 | 3,180 | -0.28% | 84 | 37 | Township |
| Berlin | 22 | 3,124 | 3,117 | -0.03% | 84 | 37 | Township |
| Casco | 23 | 2,971 | 2,807 | 1.05% | 76 | 39 | Township |
| Emmett | 24 | 2,518 | 2,516 | -0.04% | 71 | 35 | Township |
| Kenockee | 25 | 2,363 | 2,406 | -0.34% | 66 | 36 | Township |
| Capac | 26 | 1,925 | 1,988 | -0.52% | 1,036 | 2 | Village |
| Yale | 27 | 1,867 | 1,899 | -0.27% | 1,360 | 1 | City |
| Brockway | 28 | 1,864 | 1,894 | -0.27% | 55 | 34 | Township |
| Greenwood | 29 | 1,466 | 1,489 | -0.41% | 41 | 36 | Township |
| Lynn | 30 | 1,114 | 1,123 | 0% | 31 | 36 | Township |
| Memphis | 31 | 1,085 | 1,079 | 0.09% | 967 | 1 | City |
| Emmett | 32 | 234 | 239 | -0.43% | 156 | 1 | Village |
| Columbus | 33 | 159 | 169 | -1.24% | 1 | 140 | Township |
Port Huron is the largest city in St. Clair County, with a population of 28,045.
Columbus is the smallest city in St. Clair County, with a population of 159.
There are 33 cities in St. Clair County, Michigan.