| Opp, AL (City) |
| Oppelo, AR (City) |
| Oppenheim, NY (Town) |
| Ops, ND (Township) |
| Optima, OK (Town) |
| Oquawka, IL (Village) |
| Oquawka Township, IL (Township) |
| Ora, ND (Township) |
| Ora Township, IL (Township) |
| Oradell, NJ (Borough) |
| Oran, MO (City) |
| Oran Township, IA (Township) |
| Oran Township, IL (Township) |
| Orange, NY (Town) |
| Orange, MN (Township) |
