21 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Rock Creek township | 1 | 2,770 | 2,778 | -0.14% | 52 | 53.74 | Township |
| Oskaloosa township | 2 | 2,162 | 2,161 | 0.05% | 38 | 56.95 | Township |
| Delaware township | 3 | 1,779 | 1,812 | -0.56% | 20 | 87.56 | Township |
| Ozawkie township | 4 | 1,644 | 1,647 | -0.12% | 44 | 37.57 | Township |
| Union township | 5 | 1,625 | 1,655 | -0.49% | 39 | 42.12 | Township |
| Kentucky township | 6 | 1,545 | 1,542 | 0% | 42 | 36.36 | Township |
| Kaw township | 7 | 1,394 | 1,386 | 0.07% | 43 | 32.22 | Township |
| Oskaloosa | 8 | 1,068 | 1,097 | -0.56% | 1,074 | 0.99 | City |
| Valley Falls | 9 | 1,064 | 1,091 | -0.47% | 1,511 | 0.70 | City |
| Jefferson township | 10 | 1,060 | 1,073 | -0.47% | 18 | 57.80 | Township |
| Sarcoxie township | 11 | 994 | 988 | 0% | 32 | 30.70 | Township |
| Perry | 12 | 849 | 853 | -0.12% | 1,134 | 0.75 | City |
| McLouth | 13 | 821 | 855 | -0.85% | 1,425 | 0.58 | City |
| Rural township | 14 | 798 | 794 | 0% | 25 | 31.90 | Township |
| Meriden | 15 | 712 | 744 | -0.84% | 926 | 0.77 | City |
| Ozawkie | 16 | 621 | 635 | -0.48% | 2,091 | 0.30 | City |
| Nortonville | 17 | 585 | 600 | -0.51% | 1,354 | 0.43 | City |
| Winchester | 18 | 441 | 455 | -0.68% | 1,340 | 0.33 | City |
| Grantville | 19 | 230 | 206 | 1.32% | 375 | 0.61 | CDP |
| Williamstown | 20 | 200 | 129 | 6.95% | 1,709 | 0.12 | CDP |
| Perry township | 21 | 106 | 104 | 0% | 2 | 48.71 | Township |
Rock Creek township is the largest city in Jefferson County, with a population of 2,770.
Perry township is the smallest city in Jefferson County.
There are 21 cities in Jefferson County, Kansas.