| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Wildwood | 1 | 34,855 | 35,393 | -0.29% | 520 | 67 | City |
| Washington | 2 | 16,116 | 14,701 | 1.32% | 1,620 | 10 | City |
| Union | 3 | 13,651 | 12,382 | 1.53% | 1,501 | 9 | City |
| Ellisville | 4 | 10,403 | 9,987 | 0.85% | 2,383 | 4 | City |
| Pacific | 5 | 7,949 | 7,328 | 1.6% | 1,155 | 7 | City |
| Sullivan | 6 | 6,951 | 6,903 | 0.13% | 848 | 8 | City |
| St. Clair | 7 | 4,791 | 4,813 | -0.46% | 996 | 5 | City |
| Clarkson Valley | 8 | 2,526 | 2,604 | -0.55% | 937 | 3 | City |
| New Haven | 9 | 2,392 | 2,420 | -0.21% | 752 | 3 | City |
| Gerald | 10 | 1,345 | 1,370 | -0.37% | 910 | 1 | City |
| Parkway | 11 | 632 | 656 | -0.63% | 1,345 | 0 | Village |
| Berger | 12 | 271 | 269 | 0% | 863 | 0 | City |
| Lake Tekakwitha | 13 | 234 | 229 | 0.43% | 1,170 | 0 | Village |
| Leslie | 14 | 156 | 155 | 0% | 918 | 0 | Village |
| Charmwood | 15 | 16 | 16 | 0% | 114 | 0 | Town |
Wildwood is the largest city in Franklin County, with a population of 34,855.
Charmwood is the smallest city in Franklin County, with a population of 16.
There are 15 cities in Franklin County, Missouri.