14 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Arnold | 1 | 21,068 | 20,908 | 0.15% | 1,828 | 12 | City |
| Festus | 2 | 13,982 | 12,722 | 1.84% | 2,368 | 6 | City |
| De Soto | 3 | 6,517 | 6,447 | 0.22% | 1,487 | 4 | City |
| Pevely | 4 | 6,117 | 6,044 | 0.23% | 1,209 | 5 | City |
| Herculaneum | 5 | 5,472 | 4,714 | 2.84% | 1,316 | 4 | City |
| Crystal City | 6 | 4,695 | 4,735 | -0.17% | 1,009 | 5 | City |
| Hillsboro | 7 | 3,489 | 3,489 | 0% | 908 | 4 | City |
| Byrnes Mill | 8 | 3,191 | 3,179 | 0.06% | 621 | 5 | City |
| Olympian Village | 9 | 710 | 719 | -0.28% | 1,250 | 1 | City |
| Cedar Hill Lakes | 10 | 200 | 205 | -0.5% | 922 | 0 | Village |
| Scotsdale | 11 | 196 | 193 | 0% | 338 | 1 | Town |
| Parkdale | 12 | 154 | 156 | -0.65% | 1,203 | 0 | Village |
| Kimmswick | 13 | 130 | 135 | -0.76% | 556 | 0 | City |
| Peaceful Village | 14 | 96 | 93 | 0% | 490 | 0 | Village |
Arnold is the largest city in Jefferson County, with a population of 21,068.
Peaceful Village is the smallest city in Jefferson County, with a population of 96.
There are 14 cities in Jefferson County, Missouri.