| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Appleton City | 1 | 1,108 | 1,035 | 1.09% | 965 | 1 | City |
| Osceola | 2 | 1,023 | 935 | 1.09% | 948 | 1 | City |
| Lowry City | 3 | 665 | 618 | 1.22% | 648 | 1 | City |
| Collins | 4 | 136 | 126 | 1.49% | 551 | 0 | Village |
| Roscoe | 5 | 94 | 88 | 1.08% | 61 | 2 | Village |
| Vista | 6 | 37 | 35 | 0% | 282 | 0 | Village |
Appleton City is the largest city in St. Clair County, with a population of 1,108.
Vista is the smallest city in St. Clair County, with a population of 37.
There are 6 cities in St. Clair County, Missouri.