You might try looking in the
Illinois Digital Archives --
www.idaillinois.org/mainpage.html -- they have a lot of information details including a detailed early history of
Madison county which has an index. Perhaps you can find your answer there. In
Madison county there is a graveyard in the
Alton cemetery which has civil war soldiers buried in it. I believe the cemetery has been surveyed and a list of soldiers buried there is listed -- try
www.usgtombstones.org/registry.html -- that lets you pick a state and it will let you know if there is a cemetery which has been surveyed and if it has been there will be a list of names attached. Also, depending on the family, a monument might have been erected with their service dates in a family plot despite burial elsewhere. Hayner library also has a listing of cemeteries that the
Madison county genealogical society has surveyed but they are located within the library... Hopefully this helps you out and gives you a place to start while you wait for info from the archives -- and good luck to you!!!