- Ohio Camp
- Oilmont
- Old Agency
- Old Banks Place
- Old Ford Place
- Old Hellgate Village Trailer Park
- Old Town
- Old Weiss and French Place
- Old Whitcomb Place
- Olive
- Oliverville
- Ollie
- Olney
- Olson Place
- Opheim
- Opportunity
- Orchard Hills Mobile Home Park
- Orchard Homes
- Orinoco
- Oswego
- Otter
- Outback Mobile Home Settlement
- Outlook
- Ovando
- Ozan