| O Fallon Township, IL (Township) |
| O Hara Township, PA (Township) |
| O'Brien County, IA (County) |
| O'Fallon, MO (City) |
| O'Kean, AR (Town) |
| Oacoma, SD (Town) |
| Oacoma, SD (Township) |
| Oak, NE (Village) |
| Oak, KS (Township) |
| Oak, MN (Township) |
| Oak Bluffs, MA (Town) |
| Oak Brook, IL (Village) |
| Oak City, NC (Town) |
| Oak City, UT (Town) |
| Oak Creek, NE (Township) |
