This is the state site of Muster and Descriptive Rolls these are transcribed but, originals are available.
http://www.cyberdriveillinois.com/departments/archives/databases/datcivil.html
I'll have to look up where I got much of my stuff on my IL. kin. Most was prior to the internet.Seems I wrote the local County Court House. Have your friends post here and I'll see what I can do.