Harold at Midwestern Microhistory mentioned the Illinois Regional Archives Depository (IRAD) System in his blog entry here. There have been many times I've used the marriage indexes online developed by the Illinois Archives as well as the death indexes.
It was time to pay an onsite visit to the Southern Illinois University Region IRAD in Carbondale, Jackson Co., Illinois. I could research in Saline Co., Gallatin Co., Pope Co., and White Co. all in one convenient location (see map for the counties covered).
The picture of the IRAD facility was very helpful in determining if the IRAD was behind Door Number One, Two or Three....(there are other buildings in the area). Friendly and helpful graduate students will conduct your research for free; any copies made are $.25 each. Requests can be made by mail or telephone; two names per request.
The probate file of my ancestor, John S. Patillo, from Gallatin Co., IL, as well as the divorce verdict for James Patillo (John's father) and his 3rd wife, Mahala Cottan issued in Pope Co., Illinois, (both on microfilm) made the trip worthwhile. Almost every page of the Saline Co., IL, deed indexes, Volume A, Grantee, Volume A, Grantor & Volume B, both Grantee and Grantor, (actual books) were checked and items extracted.
The Illinois Archives also has a newsletter, "For the Record," online; this issue has the 2008 Accessions listed.