Note: As defined by the US Census Bureau, a city's official boundaries often extend miles beyond the city itself and may even cross county lines. As such, several thousand US cities officially exist in two or more counties (and therefore appear on multiple counties' lists of cities.)
City | Rank | 2024 Pop. | 2020 Pop. | Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Port Huron | 1 | 28,201 | 28,928 | -0.64% | 3,481 | 8.1 | City |
| Fort Gratiot charter township | 2 | 11,375 | 11,225 | -0.28% | 713 | 16.0 | Township |
| Port Huron charter township | 3 | 10,756 | 10,793 | -0.07% | 838 | 12.8 | Township |
| Marysville | 4 | 9,892 | 9,990 | -0.25% | 1,350 | 7.3 | City |
| Kimball township | 5 | 9,582 | 9,617 | -0.19% | 258 | 37.1 | Township |
| Clay township | 6 | 8,286 | 8,447 | -0.59% | 234 | 35.5 | Township |
| St. Clair township | 7 | 7,145 | 7,093 | 0.11% | 186 | 38.4 | Township |
| St. Clair | 8 | 6,009 | 5,521 | 2.07% | 2,044 | 2.9 | City |
| Clyde township | 9 | 5,442 | 5,523 | -0.18% | 153 | 35.7 | Township |
| Ira township | 10 | 4,952 | 4,980 | -0.24% | 291 | 17.0 | Township |
| Mussey township | 11 | 4,181 | 4,240 | -0.29% | 117 | 35.7 | Township |
| Columbus township | 12 | 4,109 | 4,110 | 0.15% | 112 | 36.6 | Township |
| Algonac | 13 | 4,102 | 4,192 | -0.56% | 2,891 | 1.4 | City |
| Burtchville township | 14 | 4,077 | 4,076 | 0.12% | 262 | 15.5 | Township |
| Casco township | 15 | 4,006 | 3,996 | 0.07% | 109 | 36.9 | Township |
| Marine City | 16 | 3,999 | 4,071 | -0.45% | 1,855 | 2.2 | City |
| East China township | 17 | 3,632 | 3,703 | -0.44% | 551 | 6.6 | Township |
| China township | 18 | 3,531 | 3,506 | 0.34% | 103 | 34.2 | Township |
| Cottrellville township | 19 | 3,433 | 3,413 | 0.29% | 165 | 20.9 | Township |
| Riley township | 20 | 3,207 | 3,199 | 0.25% | 84 | 38.2 | Township |
| Wales township | 21 | 3,193 | 3,176 | 0% | 85 | 37.4 | Township |
| Berlin township | 22 | 3,093 | 3,115 | -0.48% | 83 | 37.1 | Township |
| Casco township | 23 | 2,913 | 2,807 | 1.08% | 75 | 38.9 | Township |
| Emmett township | 24 | 2,530 | 2,514 | 0.2% | 72 | 35.3 | Township |
| Kenockee township | 25 | 2,388 | 2,405 | -0.17% | 67 | 35.7 | Township |
| Capac | 26 | 1,960 | 1,991 | -0.41% | 1,055 | 1.9 | Village |
| Yale | 27 | 1,887 | 1,897 | -0.16% | 1,374 | 1.4 | City |
| Brockway township | 28 | 1,887 | 1,891 | 0.21% | 56 | 33.7 | Township |
| Greenwood township | 29 | 1,503 | 1,491 | 0.87% | 42 | 35.8 | Township |
| Lynn township | 30 | 1,115 | 1,122 | -0.09% | 31 | 35.7 | Township |
| Memphis | 31 | 1,055 | 1,082 | -0.66% | 940 | 1.1 | City |
| Emmett | 32 | 235 | 238 | -0.42% | 157 | 1.5 | Village |
Note: City markers shown outside the county boundary mean that a part of the city extends into this county, but is primarily located in an adjacent county.
Port Huron is the largest city in St. Clair County.
Emmett is the smallest city in St. Clair County.
There are 32 cities in St. Clair County, Michigan.