| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Fort Atkinson | 1 | 12,346 | 12,593 | -0.34% | 2,112 | 6 | City |
| Jefferson | 2 | 7,816 | 7,783 | 0.03% | 1,340 | 6 | City |
| Lake Mills | 3 | 6,748 | 6,270 | 1.4% | 1,615 | 4 | City |
| Waterloo | 4 | 3,630 | 3,487 | 0.83% | 957 | 4 | City |
| Johnson Creek | 5 | 3,451 | 3,338 | 0.47% | 1,140 | 3 | Village |
| Palmyra | 6 | 1,719 | 1,728 | -0.06% | 750 | 2 | Village |
| Sullivan | 7 | 663 | 652 | 0% | 585 | 1 | Village |
Fort Atkinson is the largest city in Jefferson County, with a population of 12,346.
Sullivan is the smallest city in Jefferson County, with a population of 663.
There are 7 cities in Jefferson County, Wisconsin.