During the Civil War, he served with Company "G", 23rd Regiment, Connecticut Infantry during 1862-63. War Department records show three enlistments for soldiers named George W. Barnum from Connecticut. One of them enlisted 18 April 1861, giving his residence as Waterbury; the second enlisted 25 April 1861, giving his residence as New Fairfield; and the third enlisted 26 August 1862, listing his place of residence as Danbury. None of the three provided an age.
There is a Civil war flag on his gravestone.