Williams was the son of Brevet Lieutenant Colonel and Captain Bartholomew Williams (died 1797), of his Majesty's Marine Forces,A List of the officers of the Army...(1783)|Open Library| and the former Miss Anne Miller, who were married in 1756.Search Results-FamilySearch.org-Free Family History and Genealogy Records "Colonel" Bartholomew Williams, the father of the future colonel commandant, was a 40-year veteran of his Majesty's Marine Forces, figuring on the 1767 Army List as a first lieutenant of Marines on half pay, and on the Army Lists of 1778 and 1783 as a captain of Marines since November 1776. His promotion, on the Army List, to the brevet (army) rank of major was reported in the December 1790 issue of "The Scots magazine".The Scots magazine|Vol 52|James Boswell|December 1790|Deaths and Preferments|Admiralty Office Dec. 7|page 623|Google Books
