11 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Fort Atkinson | 1 | 12,196 | 12,581 | -0.63% | 2,086 | 6 | City |
| Jefferson | 2 | 7,540 | 7,805 | -0.7% | 1,293 | 6 | City |
| Lake Mills | 3 | 6,849 | 6,231 | 1.84% | 1,639 | 4 | City |
| Waterloo | 4 | 3,690 | 3,492 | 1.1% | 973 | 4 | City |
| Johnson Creek | 5 | 3,514 | 3,331 | 1.06% | 1,161 | 3 | Village |
| Ixonia | 6 | 2,174 | 1,856 | 1.73% | 598 | 4 | CDP |
| Palmyra | 7 | 1,669 | 1,729 | -0.71% | 729 | 2 | Village |
| Sullivan | 8 | 636 | 651 | -0.47% | 561 | 1 | Village |
| Rome | 9 | 555 | 647 | -1.6% | 150 | 4 | CDP |
| Hebron | 10 | 366 | 317 | 2.52% | 148 | 2 | CDP |
| Helenville | 11 | 159 | 245 | -3.64% | 287 | 1 | CDP |
Fort Atkinson is the largest city in Jefferson County, with a population of 12,196.
Helenville is the smallest city in Jefferson County, with a population of 159.
There are 11 cities in Jefferson County, Wisconsin.