- Old Field
- Old Field Mobile Home Park
- Old Forge
- Old Germania Heights
- Old Man Island
- Old Mastic
- Old Mill Mobile Home Park
- Old Orchard Cove
- Old Orchard Point
- Old Orchard Trailer Park
- Old Place
- Old Town Station
- Old Westbury
- Olean
- Olivebridge
- Oliver Island
- Oliverea
- Olivers Island
- Olmstedville
- Omar
- Omi
- Omro
- Onativia
- Onchiota
- Oneida
- Oneida Castle
- Oneida Corners
- Oneida Lake Beach East
- Oneida Lake Beach West
- Oneida Valley