24 cities
| City | County | 2026 Pop. ↓ |
|---|---|---|
| Ossian | Wells County | 3,479 |
| Osceola | St. Joseph County | 2,608 |
| Oakland City | Gibson County | 2,259 |
| Orleans | Orange County | 2,065 |
| Osgood | Ripley County | 1,591 |
| Odon | Daviess County | 1,382 |
| Owensville | Gibson County | 1,331 |
| Oxford | Benton County | 1,192 |
| Ogden Dunes | Porter County | 1,167 |
| Otterbein | Benton County | 1,141 |
| Oolitic | Lawrence County | 1,135 |
| Oldenburg | Franklin County | 649 |
| Oaktown | Knox County | 580 |
| Otwell | Pike County | 429 |
| Orland | Steuben County | 394 |
| Otter Lake | 366 | |
| Oswego | 350 | |
| Orestes | Madison County | 346 |
| Oakville | Delaware County | 306 |
| Ontario | 272 | |
| Owensburg | Greene County | 191 |
| Ora | Starke County | 167 |
| Otisco | Clark County | 135 |
| Onward | Cass County | 75 |