When John Thomas Mankamyer was born on 6 March 1867, in Larimer Township, Somerset, Pennsylvania, United States, his father, Christian S. Mankamyer Sr., was 33 and his mother, Mary Smearmount, was 30. He married Sarah Elizabeth Martz about 1903, in Larimer Township, Somerset, Pennsylvania, United States. They were the parents of at least 2 daughters. He lived in Somerset, Shaw Mines, Summit Township, Somerset, Pennsylvania, United States in 1930 and Somerset Township, Somerset, Pennsylvania, United States in 1940. He died on 18 June 1951, in Meyersdale, Somerset, Pennsylvania, United States, at the age of 84, and was buried in Meyersdale, Somerset, Pennsylvania, United States.