Have you heard of IRAD? The Illinois Regional Archive Depository? IRAD collects local government records. There are seven repositories in the state divided by region.
I have used IRAD many times in the past to request records, especially when I do not want to drive to a distant IRAD to view a couple of records. This is especially helpful when I have client work to do. It saves my clients research time and money if I mail a letter rather than drive to the archive to view a couple of records.
I sent a letter to IRAD at SIU (Southern Illinois University) a couple of weeks ago asking about a marriage record from 1813 in Madison county. Madison county at that time was about half the state. I received a copy of the marriage register confirming the date I had and additional paperwork with state resources.
Most of the paperwork I had received before. Standard stuff they send out with each response. BUT, this time they also sent me a legal size sheet of paper listing the Earliest Records in Illinois County Courthouses with notations of counties that had record losses! This is easier to carry around than The Red Book or other such book! They also sent a Counties, Townships and Ranges in Illinois legal size sheet with the counties on one side and how to order records and determine location on the other side. Fantastic resource especially for those new to land records in Illinois. They also sent a brochure about researching in the Illinois State Archives.
If you have not used the IRAD system, check them out. I have always had a quick turnaround from my letters and usually great results.