IL DMV is the worst I have worked with yet but they execute most of their transactions at a Currency Exchange so you do not really have to deal with them. Someone who flips cars in IL can maybe give some hints.
If the car is from Indiana (a whopping 15 minutes from Chicago) and registered in Indiana their BMV is quite pleasant to deal with. Unfortunately, with a neighbor like IL, there are some complications.
Any out of state vehicle has to have a VIN verification done by either law enforcement or the BMV personnel
Proof of residence is required to do anything (two paper bills) unless your drivers license is also from Indiana
Bill of Sale (use the Indiana BMV form) if the title does not include the selling price (IL titles for instance)
My county requires smog on anything made after 1976...but it is every two years so buy and odd year car now and it will never be an issue
On the plus side, I cannot stress enough how pleasant and efficient dealing with the IN BMV is. Even with the VIN verification, I think the longest I have spent there was 20 minutes.
In IL, watch of titles that have been re-assigned multiple times. This is often a practice of "title jumping" as IL lets you pay for registration and have it sent anywhere...even if you don't have title on the car. To avoid taxes, lots of low priced cars have had the title assigned (supposed to only be done by licensed retail dealers) at least a couple of times and if even one is not done correctly (from experience) this will cause headaches.
If the timing were not so I crappy I would be volunteering to help on this effort. With the combination of short'ish dwell time between Barber and Gingerman and helping transport the Nash, I just have too many things going on.