23 cities
| City | County | 2025 Pop. ↓ |
|---|---|---|
| Oshkosh | Winnebago County | 65,790 |
| Oak Creek | Milwaukee County | 37,593 |
| Onalaska | La Crosse County | 19,118 |
| Oconomowoc | Waukesha County | 18,973 |
| Oregon | Dane County | 11,980 |
| Okauchee Lake | Waukesha County | 4,757 |
| Oconto | Oconto County | 4,624 |
| Omro | Winnebago County | 3,601 |
| Oostburg | Sheboygan County | 3,121 |
| Oconto Falls | Oconto County | 3,006 |
| Osceola | Polk County | 2,934 |
| Osseo | Trempealeau County | 1,771 |
| Orfordville | Rock County | 1,490 |
| Oakfield | Fond du Lac County | 1,059 |
| Owen | Clark County | 904 |
| Oconomowoc Lake | Dodge County | 592 |
| Ontario | Vernon County | 537 |
| Oxford | Marquette County | 534 |
| Oliver | Douglas County | 417 |
| Oakdale | Monroe County | 306 |
| Ogema | Price County | 245 |
| Ogdensburg | Waupaca County | 180 |
| Odanah | Ashland County | 79 |