6 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Appleton City | 1 | 1,105 | 1,034 | 1.28% | 963 | 1.15 | City |
| Osceola | 2 | 995 | 935 | 1.22% | 922 | 1.08 | City |
| Lowry City | 3 | 666 | 616 | 1.52% | 649 | 1.03 | City |
| Collins | 4 | 135 | 127 | 1.5% | 547 | 0.25 | Village |
| Roscoe | 5 | 97 | 91 | 1.04% | 63 | 1.53 | Village |
| Vista | 6 | 37 | 34 | 2.78% | 282 | 0.13 | Village |
Appleton City is the largest city in St. Clair County, with a population of 1,105.
Vista is the smallest city in St. Clair County.
There are 6 cities in St. Clair County, Missouri.