Bruce another valuable source is the State Historical Library. It has changed allot in the past years.Online is good but,sometimes it's best to go there. Here is the link to their genealogical services.Again I had written them via U.S.postal service years ago and received some special Field Orders on my GGGrandfather 1st Lt. John F. Elliott 36IL.Inf. Co.K that were not in NARA.Of course it houses the Lincoln Presidential Library.There are many who first came to IL. that moved on into Missouri and Ark.