33 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Port Huron | 1 | 28,193 | 28,935 | -0.53% | 3,480 | 8 | City |
| Fort Gratiot charter | 2 | 11,864 | 11,229 | 1.46% | 743 | 16 | Township |
| Port Huron charter | 3 | 10,654 | 10,789 | -0.14% | 830 | 13 | Township |
| Marysville | 4 | 9,835 | 9,999 | -0.33% | 1,342 | 7 | City |
| Kimball | 5 | 9,626 | 9,620 | 0.01% | 259 | 37 | Township |
| Clay | 6 | 8,250 | 8,447 | -0.33% | 233 | 35 | Township |
| St. Clair | 7 | 7,138 | 7,098 | 0.11% | 186 | 38 | Township |
| St. Clair | 8 | 5,913 | 5,468 | 1.53% | 2,011 | 3 | City |
| Clyde | 9 | 5,417 | 5,517 | -0.26% | 152 | 36 | Township |
| Ira | 10 | 5,112 | 4,988 | 0.55% | 300 | 17 | Township |
| Casco | 11 | 4,387 | 4,018 | 1.39% | 119 | 37 | Township |
| Columbus | 12 | 4,296 | 4,126 | 0.68% | 117 | 37 | Township |
| Mussey | 13 | 4,164 | 4,239 | -0.26% | 117 | 36 | Township |
| Algonac | 14 | 4,090 | 4,192 | -0.51% | 2,882 | 1 | City |
| Burtchville | 15 | 4,037 | 4,073 | -0.05% | 260 | 16 | Township |
| Marine City | 16 | 3,989 | 4,072 | -0.42% | 1,850 | 2 | City |
| East China | 17 | 3,659 | 3,704 | 0% | 555 | 7 | Township |
| China | 18 | 3,493 | 3,503 | -0.23% | 102 | 34 | Township |
| Cottrellville | 19 | 3,484 | 3,412 | 1.34% | 167 | 21 | Township |
| Riley | 20 | 3,181 | 3,198 | -0.22% | 83 | 38 | Township |
| Wales | 21 | 3,166 | 3,180 | -0.28% | 85 | 37 | Township |
| Berlin | 22 | 3,125 | 3,117 | -0.03% | 84 | 37 | Township |
| Casco | 23 | 2,940 | 2,807 | 1.07% | 76 | 39 | Township |
| Emmett | 24 | 2,519 | 2,516 | -0.04% | 71 | 35 | Township |
| Kenockee | 25 | 2,371 | 2,406 | -0.34% | 67 | 36 | Township |
| Capac | 26 | 1,935 | 1,988 | -0.57% | 1,041 | 2 | Village |
| Yale | 27 | 1,872 | 1,899 | -0.32% | 1,363 | 1 | City |
| Brockway | 28 | 1,869 | 1,894 | -0.27% | 56 | 34 | Township |
| Greenwood | 29 | 1,472 | 1,489 | -0.41% | 41 | 36 | Township |
| Lynn | 30 | 1,114 | 1,123 | 0% | 31 | 36 | Township |
| Memphis | 31 | 1,084 | 1,079 | 0.09% | 966 | 1 | City |
| Emmett | 32 | 235 | 239 | -0.42% | 157 | 1 | Village |
| Columbus | 33 | 161 | 169 | -1.23% | 1 | 140 | Township |
Port Huron is the largest city in St. Clair County, with a population of 28,193.
Columbus is the smallest city in St. Clair County, with a population of 161.
There are 33 cities in St. Clair County, Michigan.