Joyce,
William Henson was indeed a private in company C of the 31st Illinois Infantry Regiment. He lived in Williamson County Illinois (Near St. Louis on the Illinois side of the river). He was 18 when he joined up. Was 5'8"inces tall,had black hair, black eyes and was a farmer. He joined on January 30 1864 at Marion Illinois for 3 years. Was inducted by Col. McCook at Camp Yates (on the west side of Springfield. presently the location of the campus of Sacred Heart- Griffin high school) He was musterd out on July 11, 1865 at Springfield, Illinois by Captain Hunnington. He was reported missing in action on July 22, 1864 at Atlanta, Ga. Not heard from since that time. No discharge papers exist. Hope this helps you.
FC