Thomas C. Gallagher enrolled at Olney, Richland County, Illinois on 25 Jun3 1861 for a 3-year term of service by A. M. Peterson. He was mustered into service on 28 June 1861 at Springfield, Illinois by Captain Pitcher, Company K, 21st Infantry as a Private - age 20, height 5'6", hair-dark, eyes-blue, complexion-fair, marital status-single, occupation-printer.

He was born in Logan, Hocking County, Ohio. He re-enlisted as a Veteran on 23 Dec 1863 at Ooltewah, Tennessee and was promoted to Corporal 18 Aug 1865. He mustered out 16 Dec 1865 in San Antonio, Texas.

He was married to Sarah W. Morehouse on 21 apr 1864 in Olney, Richland County, IL. They had four sons: Walter E., Bartley A., Lemuel D. and James Barr Gallagher. They divorced and he married Sarah E. Turner in 1877 at Webb City, Jasper County, Missouri. They lived in Herington, Dickinson County, Kansas and he died 10 Mar 1897 in Webb City, Missouri.