George Mason was an Episcopalian.
From: Political Graveyard website (http://politicalgraveyard.com/bio/mason.html#RIT0GNK79; viewed 7 December 2005):
Mason, George (1725-1792) - of Virginia. Born in Stafford County, Va., December 11, 1725. Brother of Thomson Mason; uncle of Stevens Thomson Mason (1760-1803); granduncle of Armistead Thomson Mason; grandfather of James Murray Mason; great-granduncle of Stevens Thomson Mason (1811-1843). Member of Virginia state legislature, 1759, 1776-80, 1786-88; member, U.S. Constitutional Convention, 1787-88. Episcopalian. Died October 7, 1792. Interment at Gunston Hall Grounds, Near Lorton, Fairfax County, Va.; statue at State Capitol Grounds, Richmond, Va. Mason counties in Ky. and W.Va. are named for him.
Note that numerous sources and authoritative references have been consulted in order to ascertain the religious affiliation of the American Founding Fathers. Note that the excerpts and references mentioned on this page are not the only references used in order to identify this person's religious affiliation.