10 cities
| City | County | 2026 Pop. ↓ |
|---|---|---|
| Johnston | Polk County | 25,537 |
| Jefferson | Greene County | 4,133 |
| Jesup | Buchanan County | 2,554 |
| Jewell Junction | Hamilton County | 1,245 |
| Janesville | Bremer County | 1,059 |
| Joice | Worth County | 203 |
| Jamaica | Guthrie County | 197 |
| Jackson Junction | Fayette County | 39 |
| Jolley | Calhoun County | 28 |
| Jacksonville | Shelby County | 7 |