He enlisted 16 August 1861, at Liberty, NY, giving his age as 18. After serving in Company "F", 56th NY for only seven months, he died in the Army Hospital at Washington, D.C. on 31 March 1862, still aged 18 years. His father Levi and brother Isaac served in the same unit.
From NY State Adjutant General's Office Registers, Vol 25: George Barnum, age 18 years, enlisted on 16 Aug 1861 at Liberty, NY, to serve for 3 years as a private in Co F 56th NY Volunteer Infantry. He was under Capt. M.S. Wells. He died of disease on 31 Mar 1862 in Washington, DC.