| Omaha Township, IL (Township) |
| Omak, WA (City) |
| Omega, GA (City) |
| Omega Township, IA (Township) |
| Omega Township, IL (Township) |
| Omer, MI (City) |
| Omnia, KS (Township) |
| Omphghent Township, IL (Township) |
| Omro, MN (Township) |
| Omro, WI (City) |
| Omro Town, WI (Town) |
| Onaga, KS (City) |
| Onaka, SD (Town) |
| Onalaska, WI (City) |
| Onalaska, TX (City) |
