OC
- 0C (disambiguation)
- Air California
- Atlantic City
- Chigwell School
- Clackamas County, Oregon
- Colchester Royal Grammar School
- Florida
- Forward Castes
- List of Old Carthusians
- Los Angeles metropolitan area
- O.C. (rapper)
- OC Transpo
- Oak Cliff
- Oakland County, Michigan
- Oaklands College
- Oakland–Alameda County Coliseum
- Oakwood College
- Oberlin College
- Occitan language
- Ocean City, Maryland
- Ocean City, New Jersey
- Ocean County, New Jersey
- Oceanside, California
- Oconee County, Georgia
- Oconee County, South Carolina
- Offensive coordinator
- Offering circular
- Officer candidate
- Officer commanding
- Officer of the Order of Canada
- Oklahoma
- Oklahoma Christian University
- Oklahoma City, Oklahoma
- Old Chinese
- Old Colwyn
- Open collector
- Optical Carrier
- Oral contraceptive
- Orange County (disambiguation)
- Orange County, California
- Orange County, Florida
- Orange County, Indiana
- Orange County, New York
- Orange County, North Carolina
- Orange County, Texas
- Orange County, Vermont
- Orange County, Virginia
- Orange, Texas
- Orbis Communications
- Order of Carmelites
- Oregon City, Oregon
- Oregon Crusaders Drum and Bugle Corps
- Orewa College
- Organ-on-a-chip
- Organisation Consul
- Organized crime
- Original character
- Orlando, Florida
- Ornithological Council
- Osceola, Indiana
- Ottawa—Carleton (federal electoral district)
- Outrigger canoe
- Overclocking
- Overcurrent
- Owens Corning
- Oxi Clean
- PGA Express
- San Diego County
- The O.C.
- The O.C. (professional wrestling)
- °C