| Onward, IN (Town) |
| Onycha, AL (Town) |
| Oolitic, IN (Town) |
| Oologah, OK (Town) |
| Oostburg Village, WI (Village) |
| Opa-locka , FL (City) |
| Opal, WY (Town) |
| Opdahl, SD (Township) |
| Opdyke West, TX (Town) |
| Opelika, AL (City) |
| Opelousas, LA (City) |
| Opheim, MT (Town) |
| Ophir, UT (Town) |
| Ophir, CO (Town) |
| Ophir Township, IL (Township) |
