When Mary Threlfall was born in October 1895, in Philadelphia Monthly Meeting, Philadelphia, Pennsylvania, United States, her father, John Threlfall, was 31 and her mother, Winifred Collins, was 26. She married Maurice J Guinan on 14 July 1920, in Philadelphia Monthly Meeting, Philadelphia, Pennsylvania, United States. They were the parents of at least 1 daughter. She lived in Philadelphia, Pennsylvania, United States for about 10 years and Upper Darby, Delaware, Pennsylvania, United States in 1920. She died on 17 December 1971, in East Lansdowne, Delaware, Pennsylvania, United States, at the age of 76.