23 cities
| City | County | 2025 Pop. ↓ |
|---|---|---|
| Oshkosh | Winnebago County | 67,324 |
| Oak Creek | Milwaukee County | 38,797 |
| Oconomowoc | Waukesha County | 20,449 |
| Onalaska | La Crosse County | 20,155 |
| Oregon | Dane County | 12,058 |
| Okauchee Lake | Waukesha County | 4,757 |
| Oconto | Oconto County | 4,642 |
| Omro | Winnebago County | 3,639 |
| Oostburg | Sheboygan County | 3,058 |
| Oconto Falls | Oconto County | 3,036 |
| Osceola | Polk County | 2,905 |
| Osseo | Trempealeau County | 1,818 |
| Orfordville | Rock County | 1,630 |
| Oakfield | Fond du Lac County | 1,066 |
| Owen | Clark County | 901 |
| Oconomowoc Lake | Dodge County | 568 |
| Oxford | Marquette County | 533 |
| Ontario | Vernon County | 525 |
| Oliver | Douglas County | 417 |
| Oakdale | Monroe County | 303 |
| Ogema | Price County | 245 |
| Ogdensburg | Waupaca County | 176 |
| Odanah | Ashland County | 79 |