| Onalaska Town, WI (Town) |
| Onamia, MN (Township) |
| Onamia, MN (City) |
| Onancock, VA (Town) |
| Onarga, IL (Village) |
| Onarga Township, IL (Township) |
| Onawa, IA (City) |
| Onaway, ID (City) |
| Onaway, MI (City) |
| One Daytona Community Development District, FL (CDD) |
| One Road, SD (Township) |
| Oneco Township, IL (Township) |
| Oneida, NY (City) |
| Oneida, IL (City) |
| Oneida, TN (Town) |
