14 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Arnold | 1 | 21,100 | 20,908 | 0.15% | 1,830 | 12 | City |
| Festus | 2 | 14,234 | 12,722 | 1.8% | 2,410 | 6 | City |
| De Soto | 3 | 6,531 | 6,447 | 0.21% | 1,490 | 4 | City |
| Pevely | 4 | 6,132 | 6,044 | 0.25% | 1,212 | 5 | City |
| Herculaneum | 5 | 5,624 | 4,714 | 2.78% | 1,353 | 4 | City |
| Crystal City | 6 | 4,687 | 4,735 | -0.17% | 1,007 | 5 | City |
| Hillsboro | 7 | 3,489 | 3,489 | 0% | 908 | 4 | City |
| Byrnes Mill | 8 | 3,194 | 3,179 | 0.09% | 621 | 5 | City |
| Olympian Village | 9 | 708 | 719 | -0.28% | 1,246 | 1 | City |
| Cedar Hill Lakes | 10 | 199 | 205 | -0.5% | 917 | 0 | Village |
| Scotsdale | 11 | 197 | 193 | 0.51% | 340 | 1 | Town |
| Parkdale | 12 | 154 | 156 | 0% | 1,203 | 0 | Village |
| Kimmswick | 13 | 129 | 135 | -0.77% | 551 | 0 | City |
| Peaceful Village | 14 | 97 | 93 | 1.04% | 495 | 0 | Village |
Arnold is the largest city in Jefferson County, with a population of 21,100.
Peaceful Village is the smallest city in Jefferson County, with a population of 97.
There are 14 cities in Jefferson County, Missouri.