The year of his birth, his family moved to Ecorse, Michigan. He served in the Union Army, 2d Brigade, 2d Division, 15th Army Corps. Enlisted at Camp Dennison in Co. B, 47th Regiment, Ohio Infantry, June 15, 1861 and re-enlisted at Cleveland, Tenn., in February, 1864. At the battle of Atlanta, July 28, 1864, he was captured and sent to Andersonville Prison, where he remained until exchanged by special order in September, 1864. He was mustered out at Camp Dennison August 13, 1865. He married Mary L. Reeves April 4, 1865. Mary was the daughter of Andrew J. and Lydia A. ( Baxter ) Reeves and the widow of Wm. R. Baker, who died at Fort Gaines on October 15, 1864. Warren and Mary had 5 children.
In the 1880 US Census for Ash Township, Monroe, Michigan the family of Warren BARNUM was enumerated as follows:
Household #179; Family #182
Barnum, Warren W.; W; M; 35; M; Farmer; b. New York; father b. Not Known; mother b. Not Known
Barnum, Mary L.; W; F; 36; Wife; M; Keeping House; b. New York; father b. N. Jersey; mother b. New York
Barnum, Lilly A.; W; F; 8; Daughter; S; At School; attended school during previous year; b. Michigan; father b. New York; mother b. New York
Barnum, Welington A.; W; M; 5; Son; S; At Home; b. Michigan; father b. New York; mother b. New York
Barnum, Floid L.; W; M; 1; Son; S; At Home; b. Michigan; father b. New York; mother b. New York
Baker, Clara; W; F; 17; Step-daughter; S; At Home; b. Michigan; father b. Michigan; mother b. New York