| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Port Huron | 1 | 28,125 | 28,930 | -0.52% | 3,471 | 8 | City |
| Fort Gratiot | 2 | 11,730 | 11,239 | 0.13% | 735 | 16 | Township |
| Port Huron | 3 | 10,659 | 10,792 | -0.06% | 831 | 13 | Township |
| Marysville | 4 | 9,835 | 9,996 | -0.33% | 1,342 | 7 | City |
| Kimball | 5 | 9,679 | 9,620 | 0.28% | 261 | 37 | Township |
| Clay | 6 | 8,261 | 8,446 | -0.08% | 233 | 35 | Township |
| St. Clair | 7 | 7,187 | 7,098 | 0.39% | 187 | 38 | Township |
| St. Clair | 8 | 5,921 | 5,464 | 1.51% | 2,014 | 3 | City |
| Clyde | 9 | 5,415 | 5,513 | -0.13% | 152 | 36 | Township |
| Ira | 10 | 5,125 | 4,986 | 0.41% | 301 | 17 | Township |
| Casco | 11 | 4,446 | 4,018 | 1.34% | 121 | 37 | Township |
| Columbus | 12 | 4,337 | 4,127 | 0.79% | 118 | 37 | Township |
| Mussey | 13 | 4,174 | 4,240 | -0.07% | 117 | 36 | Township |
| Algonac | 14 | 4,089 | 4,191 | -0.49% | 2,882 | 1 | City |
| Burtchville | 15 | 4,030 | 4,073 | -0.1% | 259 | 16 | Township |
| Marine City | 16 | 3,980 | 4,071 | -0.43% | 1,846 | 2 | City |
| East China | 17 | 3,660 | 3,706 | -0.03% | 555 | 7 | Township |
| China | 18 | 3,557 | 3,504 | 0.76% | 104 | 34 | Township |
| Cottrellville | 19 | 3,500 | 3,412 | 0.89% | 168 | 21 | Township |
| Wales | 20 | 3,223 | 3,179 | 0.88% | 86 | 37 | Township |
| Riley | 21 | 3,201 | 3,200 | 0.16% | 84 | 38 | Township |
| Berlin | 22 | 3,142 | 3,116 | 0.26% | 85 | 37 | Township |
| Casco | 23 | 2,968 | 2,806 | 1.06% | 76 | 39 | Township |
| Emmett | 24 | 2,510 | 2,516 | -0.2% | 71 | 35 | Township |
| Kenockee | 25 | 2,375 | 2,405 | -0.04% | 67 | 36 | Township |
| Capac | 26 | 1,932 | 1,987 | -0.57% | 1,040 | 2 | Village |
| Brockway | 27 | 1,888 | 1,892 | 0.43% | 56 | 34 | Township |
| Yale | 28 | 1,867 | 1,898 | -0.32% | 1,360 | 1 | City |
| Greenwood | 29 | 1,467 | 1,490 | -0.41% | 41 | 36 | Township |
| Lynn | 30 | 1,113 | 1,122 | 0% | 31 | 36 | Township |
| Memphis | 31 | 1,091 | 1,077 | 0% | 972 | 1 | City |
| Emmett | 32 | 235 | 239 | -0.42% | 157 | 1 | Village |
| Columbus | 33 | 163 | 169 | -0.61% | 1.0 | 140 | Township |
Port Huron is the largest city in St. Clair County, with a population of 28,125.
Columbus is the smallest city in St. Clair County, with a population of 163.
There are 33 cities in St. Clair County, Michigan.