Thomas Gilliland was the son of Thomas Gilliland and Ann Thomas.
According to William's Revolutionary War Pension, in November 1776, while residing in St. Paul's Parish, he enrolled in the militia of Wilkes County, Georgia. He served four months in each of the years 1777, 1778, and 1779, and two months in 1780. After the war, he moved with his father to Wilkes County.
William appeared on the 1785 Tax Digest for Wilkes County in Captain Walker's District with taxable property of 1 poll and 287½ acres.
William Gilliland married Susan Grantham on 10 March 1792 at Warren County, Georgia, (date provided by Susan Gilliland and the testimony of two witnesses, in Revolutionary War pension files.