10 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Oskaloosa | 1 | 1,068 | 1,097 | -0.56% | 1,074 | 0.99 | City |
| Valley Falls | 2 | 1,064 | 1,091 | -0.47% | 1,511 | 0.70 | City |
| Perry | 3 | 849 | 853 | -0.12% | 1,134 | 0.75 | City |
| McLouth | 4 | 821 | 855 | -0.84% | 1,425 | 0.58 | City |
| Meriden | 5 | 712 | 744 | -0.84% | 926 | 0.77 | City |
| Ozawkie | 6 | 621 | 635 | -0.48% | 2,091 | 0.30 | City |
| Nortonville | 7 | 585 | 600 | -0.51% | 1,354 | 0.43 | City |
| Winchester | 8 | 441 | 455 | -0.68% | 1,340 | 0.33 | City |
| Grantville | 9 | 230 | 206 | 1.32% | 375 | 0.61 | CDP |
| Williamstown | 10 | 200 | 129 | 6.95% | 1,709 | 0.12 | CDP |
Oskaloosa is the largest city in Jefferson County, with a population of 1,068.
Williamstown is the smallest city in Jefferson County.
There are 10 cities in Jefferson County, Kansas.