Cities in United States ( 10,163 )
- Oelwein
- O'Fallon, Illinois
- O'Fallon, Missouri
- Offutt Air Force Base
- Ogallala, Nebraska
- Ogden, North Carolina
- Ogden, Utah
- Ogdensburg, New York
- Oglesby, Illinois
- Ohioville
- Oil City, Pennsylvania
- Oildale
- Ojai
- Ojus
- Okanogan, Washington
- Okauchee Lake
- Okeechobee, Florida
- Okemah
- Okemos
- Oklahoma City
- Okmulgee, Oklahoma
- Okolona, Kentucky
- Okolona, Mississippi
- Olathe, Kansas
- Old Bethpage
- Old Bridge, New Jersey
- Old Forge, Pennsylvania
- Old Greenwich
- Old Jefferson
- Old Mystic
- Old Orchard Beach
- Old Saybrook
- Old Tappan
- Old Town, Maine
- Old Westbury
- Oldsmar