12 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Appleton City | 1 | 1,092 | 1,023 | 1.11% | 951 | 1 | City |
| Appleton City | 2 | 1,092 | 1,030 | 1.11% | 951 | 1 | City |
| Osceola | 3 | 990 | 928 | 1.12% | 918 | 1 | City |
| Osceola | 4 | 990 | 935 | 1.12% | 918 | 1 | City |
| Lowry City | 5 | 660 | 613 | 1.23% | 643 | 1 | City |
| Lowry City | 6 | 660 | 617 | 1.23% | 643 | 1 | City |
| Collins | 7 | 134 | 125 | 0.75% | 543 | 0 | Village |
| Collins | 8 | 134 | 126 | 0.75% | 543 | 0 | Village |
| Roscoe | 9 | 94 | 88 | 1.08% | 61 | 2 | Village |
| Roscoe | 10 | 94 | 89 | 1.08% | 61 | 2 | Village |
| Vista | 11 | 37 | 35 | 0% | 282 | 0 | Village |
| Vista | 12 | 37 | 35 | 0% | 282 | 0 | Village |
Appleton City is the largest city in St. Clair County, with a population of 1,092.
Vista is the smallest city in St. Clair County, with a population of 37.
There are 12 cities in St. Clair County, Missouri.