32 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Port Huron | 1 | 28,019 | 28,928 | -0.65% | 3,458 | 8.10 | City |
| Fort Gratiot charter township | 2 | 11,343 | 11,225 | -0.28% | 711 | 15.96 | Township |
| Port Huron charter township | 3 | 10,749 | 10,793 | -0.07% | 838 | 12.83 | Township |
| Marysville | 4 | 9,868 | 9,990 | -0.24% | 1,347 | 7.33 | City |
| Kimball township | 5 | 9,564 | 9,617 | -0.19% | 258 | 37.12 | Township |
| Clay township | 6 | 8,237 | 8,447 | -0.59% | 232 | 35.48 | Township |
| St. Clair township | 7 | 7,153 | 7,093 | 0.11% | 186 | 38.40 | Township |
| St. Clair | 8 | 6,131 | 5,521 | 2.03% | 2,085 | 2.94 | City |
| Clyde township | 9 | 5,432 | 5,523 | -0.18% | 152 | 35.65 | Township |
| Ira township | 10 | 4,940 | 4,980 | -0.24% | 290 | 17.04 | Township |
| Mussey township | 11 | 4,169 | 4,240 | -0.29% | 117 | 35.68 | Township |
| Columbus township | 12 | 4,115 | 4,110 | 0.15% | 112 | 36.65 | Township |
| Burtchville township | 13 | 4,082 | 4,076 | 0.12% | 263 | 15.55 | Township |
| Algonac | 14 | 4,080 | 4,192 | -0.54% | 2,875 | 1.42 | City |
| Casco township | 15 | 4,009 | 3,996 | 0.07% | 109 | 36.88 | Township |
| Marine City | 16 | 3,981 | 4,071 | -0.45% | 1,846 | 2.16 | City |
| East China township | 17 | 3,616 | 3,703 | -0.44% | 548 | 6.59 | Township |
| China township | 18 | 3,543 | 3,506 | 0.34% | 104 | 34.18 | Township |
| Cottrellville township | 19 | 3,443 | 3,413 | 0.29% | 165 | 20.85 | Township |
| Riley township | 20 | 3,215 | 3,199 | 0.25% | 84 | 38.24 | Township |
| Wales township | 21 | 3,193 | 3,176 | 0% | 85 | 37.37 | Township |
| Berlin township | 22 | 3,078 | 3,115 | -0.48% | 83 | 37.13 | Township |
| Casco township | 23 | 2,944 | 2,807 | 1.06% | 76 | 38.87 | Township |
| Emmett township | 24 | 2,535 | 2,514 | 0.2% | 72 | 35.33 | Township |
| Kenockee township | 25 | 2,384 | 2,405 | -0.17% | 67 | 35.65 | Township |
| Capac | 26 | 1,952 | 1,991 | -0.41% | 1,051 | 1.86 | Village |
| Brockway township | 27 | 1,891 | 1,891 | 0.21% | 56 | 33.67 | Township |
| Yale | 28 | 1,885 | 1,897 | -0.11% | 1,373 | 1.37 | City |
| Greenwood township | 29 | 1,516 | 1,491 | 0.86% | 42 | 35.80 | Township |
| Lynn township | 30 | 1,114 | 1,122 | -0.09% | 31 | 35.72 | Township |
| Memphis | 31 | 1,048 | 1,082 | -0.66% | 934 | 1.12 | City |
| Emmett | 32 | 234 | 238 | -0.43% | 156 | 1.50 | Village |
Port Huron is the largest city in St. Clair County, with a population of 28,019.
Emmett is the smallest city in St. Clair County.
There are 32 cities in St. Clair County, Michigan.