23 cities
| City | County | 2026 Pop. ↓ |
|---|---|---|
| Oshkosh | Winnebago County | 67,406 |
| Oak Creek | Milwaukee County | 39,222 |
| Oconomowoc | Waukesha County | 20,897 |
| Onalaska | La Crosse County | 20,413 |
| Oregon | Dane County | 12,222 |
| Okauchee Lake | Waukesha County | 4,920 |
| Oconto | Oconto County | 4,647 |
| Omro | Winnebago County | 3,635 |
| Oostburg | Sheboygan County | 3,058 |
| Oconto Falls | Oconto County | 3,049 |
| Osceola | Polk County | 2,931 |
| Osseo | Trempealeau County | 1,818 |
| Orfordville | Rock County | 1,662 |
| Oakfield | Fond du Lac County | 1,068 |
| Owen | Clark County | 899 |
| Oconomowoc Lake | Dodge County | 568 |
| Oxford | Marquette County | 533 |
| Ontario | Vernon County | 524 |
| Oliver | Douglas County | 417 |
| Oakdale | Monroe County | 304 |
| Ogema | Price County | 276 |
| Ogdensburg | Waupaca County | 174 |
| Odanah | Ashland County | 145 |