6 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Appleton City | 1 | 1,105 | 1,030 | 1.19% | 963 | 1 | City |
| Osceola | 2 | 1,001 | 935 | 1.11% | 928 | 1 | City |
| Lowry City | 3 | 669 | 617 | 1.36% | 652 | 1 | City |
| Collins | 4 | 136 | 126 | 1.49% | 551 | 0 | Village |
| Roscoe | 5 | 95 | 89 | 1.06% | 62 | 2 | Village |
| Vista | 6 | 38 | 35 | 2.7% | 290 | 0 | 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, with a population of 38.
There are 6 cities in St. Clair County, Missouri.