Mary Thornton was born in Kilbaha, Newtownsandes, Co. Kerry in 1901, the eldest of the 13 children of Myles Thornton and Mary McAuliffe. She was a granddaughter of Jim Thornton and Norrie Cunningham of Kilbaha.
Mamie emigrated to the United States in 1923. She lived in New York where she died in 1957. She never married.