29 cities
| City | County | 2026 Pop. ↓ |
|---|---|---|
| Oxford | Butler County | 22,354 |
| Oregon | Lucas County | 19,626 |
| Oakwood | Paulding County | 9,318 |
| Olmsted Falls | Cuyahoga County | 8,687 |
| Oberlin | Lorain County | 8,599 |
| Orrville | Wayne County | 8,432 |
| Obetz | Franklin County | 8,197 |
| Ontario | Richland County | 6,638 |
| Ottawa Hills | Lucas County | 4,800 |
| Ottawa | Putnam County | 4,402 |
| Orange | Cuyahoga County | 3,602 |
| Oakwood | Paulding County | 3,461 |
| Oak Harbor | Ottawa County | 2,775 |
| Orwell | Ashtabula County | 1,508 |
| Oak Hill | Jackson County | 1,400 |
| Ostrander | Delaware County | 1,291 |
| Ottoville | Putnam County | 968 |
| Owensville | Clermont County | 828 |
| Ohio City | Van Wert County | 642 |
| Oakwood | Paulding County | 534 |
| Olde West Chester | Butler County | 384 |
| Osgood | Darke County | 297 |
| Orient | Pickaway County | 257 |
| Old Washington | Guernsey County | 221 |
| Orangeville | Trumbull County | 168 |
| Oceola | Crawford County | 137 |
| Old Fort | Seneca County | 118 |
| Otway | Scioto County | 87 |
| Octa | Fayette County | 57 |