35 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Wildwood | 1 | 34,492 | 35,389 | -0.52% | 517 | 67 | City |
| Washington | 2 | 15,947 | 14,704 | 1.59% | 1,603 | 10 | City |
| Union | 3 | 13,404 | 12,394 | 1.53% | 1,474 | 9 | City |
| Ellisville | 4 | 9,681 | 9,981 | -0.62% | 2,218 | 4 | City |
| Pacific | 5 | 7,734 | 7,283 | 1.18% | 1,131 | 7 | City |
| Sullivan | 6 | 6,769 | 6,918 | -0.44% | 826 | 8 | City |
| St. Clair | 7 | 4,662 | 4,797 | -0.58% | 970 | 5 | City |
| Union | 8 | 3,187 | 3,435 | -1.51% | 31 | 103 | Township |
| Villa Ridge | 9 | 3,055 | 3,179 | 0.93% | 622 | 5 | CDP |
| Gray Summit | 10 | 2,541 | 2,383 | -0.43% | 330 | 8 | CDP |
| Clarkson Valley | 11 | 2,501 | 2,605 | -0.83% | 928 | 3 | City |
| New Haven | 12 | 2,367 | 2,422 | -0.46% | 737 | 3 | City |
| Washington | 13 | 2,340 | 2,311 | 0.56% | 66 | 36 | Township |
| Union | 14 | 2,224 | 2,150 | 0.95% | 61 | 36 | Township |
| Union | 15 | 2,101 | 2,149 | -0.52% | 46 | 45 | Township |
| Washington | 16 | 1,805 | 1,816 | -0.5% | 38 | 48 | Township |
| Gerald | 17 | 1,328 | 1,363 | -0.52% | 899 | 1 | City |
| LaBarque Creek | 18 | 1,112 | 1,165 | -2.63% | 63 | 18 | CDP |
| Lake St. Clair | 19 | 1,056 | 692 | 7.1% | 1,459 | 1 | CDP |
| Parkway | 20 | 640 | 665 | -0.78% | 1,362 | 0 | Village |
| Union | 21 | 507 | 506 | -0.2% | 14 | 36 | Township |
| Stanton | 22 | 395 | 249 | 7.05% | 121 | 3 | CDP |
| Union | 23 | 393 | 431 | -2.48% | 8 | 47 | Township |
| Union | 24 | 387 | 381 | 0.26% | 11 | 37 | Township |
| Washington | 25 | 374 | 376 | 0.27% | 7 | 57 | Township |
| Washington | 26 | 263 | 290 | -2.59% | 6 | 47 | Township |
| Berger | 27 | 259 | 259 | 0% | 825 | 0 | City |
| Lake Tekakwitha | 28 | 237 | 231 | 0.42% | 1,185 | 0 | Village |
| Washington | 29 | 167 | 165 | 0.6% | 5 | 36 | Township |
| Washington | 30 | 153 | 147 | 1.32% | 4 | 36 | Township |
| Washington | 31 | 151 | 152 | -0.66% | 7 | 21 | Township |
| Leslie | 32 | 149 | 153 | -0.67% | 4 | 36 | Township |
| Leslie | 33 | 135 | 135 | 0% | 794 | 0 | Village |
| Washington | 34 | 98 | 91 | 2.08% | 3 | 36 | Township |
| Charmwood | 35 | 16 | 16 | 0% | 114 | 0 | Town |
Wildwood is the largest city in Franklin County, with a population of 34,492.
Charmwood is the smallest city in Franklin County, with a population of 16.
There are 35 cities in Franklin County, Missouri.