William Preston was born on Christmas Day in 1729, in Limavady, Ireland, to Col. John Preston and his wife, Elizabeth. Elizabeth's father, Henry Patton, was a prominent shipwright and merchant, and her brother, James Patton, served with distinction in the Royal Navy. The Crown granted him between 100,000 and 120,000 acres in America to permit British colonization beyond the Blue Ridge Mountains. The family immigrated to Augusta County, Virginia in 1738. Subsequent French and Indian resistance and reversal of British policy limited the impact of the family's grants, but Prestonsburg, Kentucky was named in John's honor. In 1755, William survived the Draper's Meadow massacre, an attack by the Shawnee against a settlement that was part of a property (later known as Smithfield Plantation), that he inherited from his uncle, Colonel James Patton, who died in the incident.