15 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Wildwood | 1 | 34,928 | 35,390 | -0.22% | 521 | 67 | City |
| Washington | 2 | 15,932 | 14,699 | 1.31% | 1,601 | 10 | City |
| Union | 3 | 13,600 | 12,393 | 1.5% | 1,496 | 9 | City |
| Ellisville | 4 | 10,546 | 9,984 | 0.9% | 2,416 | 4 | City |
| Pacific | 5 | 8,087 | 7,351 | 1.54% | 1,175 | 7 | City |
| Sullivan | 6 | 6,933 | 6,908 | 0.06% | 846 | 8 | City |
| St. Clair | 7 | 4,706 | 4,831 | -0.44% | 979 | 5 | City |
| Clarkson Valley | 8 | 2,531 | 2,608 | -0.51% | 939 | 3 | City |
| New Haven | 9 | 2,388 | 2,421 | -0.21% | 751 | 3 | City |
| Gerald | 10 | 1,350 | 1,376 | -0.3% | 913 | 1 | City |
| Parkway | 11 | 634 | 658 | -0.63% | 1,349 | 0 | Village |
| Berger | 12 | 269 | 268 | 0% | 857 | 0 | City |
| Lake Tekakwitha | 13 | 237 | 233 | 0.42% | 1,185 | 0 | Village |
| Leslie | 14 | 157 | 154 | 0.64% | 924 | 0 | Village |
| Charmwood | 15 | 16 | 16 | 0% | 114 | 0 | Town |
Wildwood is the largest city in Franklin County, with a population of 34,928.
Charmwood is the smallest city in Franklin County, with a population of 16.
There are 15 cities in Franklin County, Missouri.