10 cities
| City | County | 2025 Pop. ↓ |
|---|---|---|
| Johnston | Polk County | 24,992 |
| Jefferson | Greene County | 4,046 |
| Jesup | Buchanan County | 2,553 |
| Jewell Junction | Hamilton County | 1,166 |
| Janesville | Bremer County | 1,057 |
| Joice | Worth County | 200 |
| Jamaica | Guthrie County | 197 |
| Jackson Junction | Fayette County | 40 |
| Jolley | Calhoun County | 29 |
| Jacksonville | Shelby County | 5 |