10 cities
| City | County | 2025 Pop. ↓ |
|---|---|---|
| Johnston | Polk County | 25,279 |
| Jefferson | Greene County | 4,140 |
| Jesup | Buchanan County | 2,547 |
| Jewell Junction | Hamilton County | 1,239 |
| Janesville | Bremer County | 1,055 |
| Joice | Worth County | 204 |
| Jamaica | Guthrie County | 196 |
| Jackson Junction | Fayette County | 38 |
| Jolley | Calhoun County | 28 |
| Jacksonville | Shelby County | 5 |