When Mahlon Nelson Thatcher was born on 8 July 1808, in Hunterdon, New Jersey, United States, his father, John Thatcher, was 30 and his mother, Rachel, was 28. He married Catherine Rittenhouse about 1832, in Hunterdon, New Jersey, United States. They were the parents of at least 3 sons and 4 daughters. He lived in Kingwood Township, Hunterdon, New Jersey, United States in 1860 and Kingwood, Hunterdon, New Jersey, United States for about 10 years. He died on 19 December 1889, in Frenchtown, Hunterdon, New Jersey, United States, at the age of 81, and was buried in Frenchtown, Hunterdon, New Jersey, United States.