30 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 |
| Union | 8 | 3,246 | 3,434 | -0.37% | 31 | 103 | Township |
| Clarkson Valley | 9 | 2,531 | 2,608 | -0.51% | 939 | 3 | City |
| New Haven | 10 | 2,388 | 2,421 | -0.21% | 751 | 3 | City |
| Washington | 11 | 2,328 | 2,314 | 0.09% | 66 | 36 | Township |
| Union | 12 | 2,174 | 2,154 | -0.18% | 60 | 36 | Township |
| Union | 13 | 1,981 | 2,148 | -2.37% | 44 | 45 | Township |
| Washington | 14 | 1,809 | 1,813 | -0.17% | 38 | 48 | Township |
| Gerald | 15 | 1,350 | 1,376 | -0.3% | 913 | 1 | City |
| Parkway | 16 | 634 | 658 | -0.63% | 1,349 | 0 | Village |
| Union | 17 | 507 | 507 | -0.2% | 14 | 36 | Township |
| Union | 18 | 393 | 429 | -1.5% | 8 | 47 | Township |
| Union | 19 | 378 | 380 | -0.53% | 10 | 37 | Township |
| Washington | 20 | 362 | 378 | -1.36% | 6 | 57 | Township |
| Berger | 21 | 269 | 268 | 0% | 857 | 0 | City |
| Washington | 22 | 262 | 287 | -1.5% | 6 | 47 | Township |
| Lake Tekakwitha | 23 | 237 | 233 | 0.42% | 1,185 | 0 | Village |
| Washington | 24 | 163 | 163 | 0.62% | 5 | 36 | Township |
| Leslie | 25 | 159 | 151 | 1.92% | 4 | 36 | Township |
| Leslie | 26 | 157 | 154 | 0.64% | 924 | 0 | Village |
| Washington | 27 | 153 | 152 | 0% | 7 | 21 | Township |
| Washington | 28 | 148 | 146 | 0% | 4 | 36 | Township |
| Washington | 29 | 92 | 91 | 0% | 3 | 36 | Township |
| Charmwood | 30 | 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 30 cities in Franklin County, Missouri.