| Otterville, MO (City) |
| Otto, MN (Township) |
| Otto, NY (Town) |
| Otto Township, IL (Township) |
| Otto Township, MI (Township) |
| Otto Township, PA (Township) |
| Ottosen, IA (City) |
| Ottoville, OH (Village) |
| Ottumwa, KS (Township) |
| Ottumwa, IA (City) |
| Otway, OH (Village) |
| Ouachita County, AR (County) |
| Ouachita Parish, LA (County) |
| Oulu Town, WI (Town) |
| Ouray, CO (City) |
