- 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
- Olivebridge
- Oliver Island
- Oliverea
- Olivers Island
- Olmstedville
- Omar
- Omi
- Omro
- Onativia
- Onchiota
- Oneida Corners
- Oneida Lake Beach East
- Oneida Lake Beach West
- Oneida Valley
- Oneida Village Mobile Home Park
- Oniontown
- Oniontown
- Onondaga Castle
- Onondaga Hill
- Onoville
- Ontário