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- Harry Oakes, discovered second-largest gold mine in Canada. Later mysteriously murdered in the Bahamas which became basis of several books and movies; born in Sangerville
- Jeremiah O'Brien (1744–1818), naval officer of the American Revolutionary War; born in Kittery
- John O'Hurley (born 1954), actor, voice actor, TV personality; J. Peterman on Seinfeld; born in Kittery
Read more about this topic: List Of People From Maine