| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Arnold | 1 | 21,029 | 20,907 | 0.17% | 1,824 | 12 | City |
| Festus | 2 | 14,318 | 12,787 | 1.79% | 2,425 | 6 | City |
| De Soto | 3 | 6,545 | 6,455 | 0.28% | 1,494 | 4 | City |
| Pevely | 4 | 6,260 | 6,059 | 0.34% | 1,238 | 5 | City |
| Herculaneum | 5 | 5,555 | 4,695 | 2.83% | 1,336 | 4 | City |
| Crystal City | 6 | 4,687 | 4,736 | -0.15% | 1,007 | 5 | City |
| Hillsboro | 7 | 3,493 | 3,490 | 0% | 909 | 4 | City |
| Byrnes Mill | 8 | 3,185 | 3,178 | 0.06% | 620 | 5 | City |
| Olympian Village | 9 | 708 | 719 | -0.28% | 1,246 | 1 | City |
| Cedar Hill Lakes | 10 | 202 | 207 | -0.49% | 931 | 0 | Village |
| Scotsdale | 11 | 198 | 193 | 0% | 341 | 1 | Town |
| Parkdale | 12 | 155 | 156 | -0.64% | 1,211 | 0 | Village |
| Kimmswick | 13 | 132 | 135 | -0.75% | 564 | 0 | City |
| Peaceful Village | 14 | 97 | 94 | 0% | 495 | 0 | Village |
Arnold is the largest city in Jefferson County, with a population of 21,029.
Peaceful Village is the smallest city in Jefferson County, with a population of 97.
There are 14 cities in Jefferson County, Missouri.