According to Official roster of the soldiers of the State of Ohio in the War of the Rebellion, 1861-1865
Thomas Irwin enlisted at age 66 as a Private in Company "A" 13th Ohio Infantry. He entered service on April 22, 1861 for 3 months service. He was mustered out on June 20, 1861. (also states service in Company "E" 13th OVI for 3 years service.
Name: Thomas Irwin Enlistment Date: 22 Apr 1861 Side Served: UnionState Served: Ohio Service Record: Enlisted as a Private on 22 April 1861 at the age of 44. Mustered in Company A, 13th Ohio Infantry Regimenton 3 May 1861. Mustered Out Company A, 13th Ohio Infantry Regiment on 20 Jun 1861. Enlisted in Company E, 13th Ohio Infantry Regiment on 26 Jun 1861. Received a disability discharge from Company E,on 12 Jan 1862.