He served with Company "D", 26th Regiment, Michigan Infantry from August 11, 1862 to June 4, 1865 and was wounded at the Battle of Spotsylvania Court House (May 8-19, 1864). According to Veterans Administration records, he also served as a private in Companies "I" and "K" of the 26th Michigan Infantry. His widow received a pension as an Army widow.
Spotsylvania represented the failure of the Union Army to smash or outflank Confederate forces defending Richmond, Virginia, during the Civil War. Following the Battle of the Wilderness (May 5-6), Union General Ulysses S. Grant moved his left flank forward, engaging the Confederate forces of General Robert E. Lee at Spotsylvania Court House, Virginia. The battle raged for about a week and a half, and on May 20 Grant continued his march southeastward in a flanking movement toward the Confederate capital. His casualties were 17,000; Lee's, 8, 000.
The Barnum Family, 1517-1904 calls him Judge S. Barnum. He is listed as a steamship passenger in 1897 on a voyage from Liverpool to Philadelphia.
From The Political Graveyard: Index to Politicians: Barnum, Judge R. — Candidate for Michigan state senate 15th District, 1910. Burial location unknown.