O
- John W. O'Daniel, United States Army general, commander of the Third Infantry Division during World War II
- Christine O'Donnell (born 1969), Republican candidate for Senate in 2006, 2008, and 2010.
- Montell Owens, professional football player.
- Mehmet Oz, surgeon, television personality. Attended Tower Hill School.
Read more about this topic: List Of People From Delaware