Joanna, it would be good idea to order this soldier's record. There will surely be a POW record indicating his date of death and place of burial (usually in what is now a National Cemetery); also, Union POW records occasionally report a prisoner's age and nativity, and other information.

For genealogical researchers, having a Civil War ancestor who was a prisoner of war is a blessing (very bad for the soldier, though!) because Union records are generally much more informative than Confederate records.