When William Marion Heaslet Sr was born in 1740, in Shippensburg, Cumberland, Pennsylvania, United States, his father, James Heaslet, was 20 and his mother, Mary Ann McCracken, was 27. He married Margaret Mary Clark on 6 April 1762, in Lancaster, Pennsylvania, United States. They were the parents of at least 3 sons and 4 daughters. He died on 4 January 1819, in Knox, Tennessee, United States, at the age of 79.
English: habitational name from Haseley (Warwickshire), Great or Little Haseley (Oxfordshire), or North Heasley in North Molton (Devon). The placenames derive from Old English hæsel ‘hazel’ + lēah ‘woodland clearing’.
Irish (Down and Louth): variant of Hazlett .