He married Mary Susan Washburn on 5 September 1886 in Hamilton County, Ohio. Mary was born 28 September 1866 in Vinton, Gallia County, Ohio. She was the oldest child of Francis Marion Washburn and Lovina Matthews.
After their marriage, George and Mary lived in Cincinnati, Ohio; Boone County, Kentucky and Rising Sun, Indiana.
George died on 31 March 1917 in Rising Sun. Mary died on 19 April 1919 in Cincinnati. According to their death certificates they were both buried in Rising Sun, but no burial record has been found for either of them.
George and Mary had 9 children:
- Joseph Mills Hillis born 24 Dec 1887 in Cincinnati. He died 3 May 1974 in El Dorado, Kansas. He married Margaret Daniel (abt 1898 - ?).
- Francis Marion Hillis born 13 Dec 1888 in Cincinnati. He died 12 Oct 1977 in Rising Sun. He married Mary Ann Johnston (11 Sep 1883 - 25 Aug 1951).
- Sylvia C Hillis born 13 Aug 1892 in Kentucky. She died 21 Mar 1970 in Kenton County, Kentucky. She married 1st Sidney Sayers Clements (19 Jan 1891 - 5 Jul 1940) and 2nd a Mr. Lawson.
- Alice Susan Hillis born 1 Apr 1896 in Rabbit Hash, Kentucky. She died 31 Jul 1979 in Hamilton County, Ohio. She married Dewey Francis Bascom (6 May 1898 - 2 Jun 1975).
- Vallie I Hillis born 16 Nov 1898 in Indiana. She died 14 Jan 1994 in Rising Sun. She married Fred Hess (4 Jul 1890 - 6 Mar 1966).
- George Raymond Hillis born 17 Jul 1900 in Indiana. He died 29 Jun 1973 in Cincinnati. He married Dorothy York.
- Barret Guy Hillis born 30 Dec 1906 in Rising Sun. He died 15 Jul 1995 in Montgomery, Ohio. He married Gladys B Griffith.
- Unnamed child born 8 April 1908 and died 7 Jul 1909 in Ohio County, Indiana.
- Willard Hillis stillborn 29 Feb 1912.