Indiana Cities
- Oak Forest, IN
- Oak Grove, IN
- Oak Hill, IN
- Oak Park, IN
- Oak Tree Crossroads, IN
- Oakford, IN
- Oakland City, IN
- Oaktown, IN
- Oakville, IN
- Oakwood, IN
- Oakwood Park, IN
- Oatsville, IN
- Ober, IN
- Occident, IN
- Ockley, IN
- Octagon, IN
- Odell, IN
- Odon, IN
- Ogden, IN
- Ogden Dunes, IN
- Ogilville, IN
- Old Bargersville, IN
- Old Bath, IN
- Old Halfway, IN
- Old Hill, IN
- Old Milan, IN
- Old Saint Louis, IN
- Old Tip Town, IN
- Old Town, IN
- Oldenburg, IN
- Olean, IN
- Olin, IN
- Olive, IN
- Oliver, IN
- Omega, IN
- Ontario, IN
- Onward, IN
- Oolitic, IN
- Ora, IN
- Orange, IN
- Orangeville, IN
- Orchard Grove, IN
- Orchard Heights Addition, IN
- Orchard Highlands, IN
- Orchard Park, IN
- Orestes, IN
- Organ Springs, IN
- Oriole, IN
- Orland, IN
- Orleans, IN
- Ormas, IN
- Orrville, IN
- Osborn Landing, IN
- Osceola, IN
- Osgood, IN
- Ossian, IN
- Oswego, IN
- Otis, IN
- Otisco, IN
- Otsego Center, IN
- Otter Village, IN
- Otterbein, IN
- Otto, IN
- Otwell, IN
- Owasco, IN
- Owen, IN
- Owensburg, IN
- Owensville, IN
- Oxford, IN
