Mary Margaret Hollen's parents were Thomas Elmer Hollen and Mary Philamenia Morrin, residents of Westmoreland County, Pennsylvania. Mrs. Hollen died in 1960, at which time she was divorced, according to her death record. She was a Registered Nurse, according to her obituary. Thomas E. Hollen died in 1965.

At the time of the 1940 census, the family lived on Painter Street, Hempfield Township, Westmoreland County. The father, Thomas E., age 43, worked for the railroad. In the home with Thomas and his wife, Mary P., 45, were Francis, 13, Mary M., 11, Bridgett A., 10, Eleanor R., 9, and Elizabeth K., 4.

Mary Margaret Hollen graduated from Jeannette High School, Westmoreland County, in 1946.