I actually just went through the same process last month, applying for my Illinois license coming from Iowa! I can relate, it is a frustrating process mostly because it's nearly impossible to get ahold of any person in the IDFPR to ask any questions... I have succeeded a few time though after waiting on hold for 20+ minutes. I think if you do the fingerprint cards you have to use the official IL ones- I got one by writing (snail mail style) the IDFPR and actually received one in the mail after about a week or so. This was before I realized there were actual people there you could talk to, but you had to have some serious patience and stay on hold. I took the card to my local police station, was printed for $10, but then had a hard time finding out where I could send the card to have it processed. I think Dekalb may have been an option, but there was another fee to have them process it. So, in the essence of time, I ended up going to an actual Livescan fingerprinter (there's one in Davenport if you're close-by) to have them done electronically, and I would recommend doing it this way if you can! It was $50, but very easy and took a whole 15 minutes. They send your prints directly to the IL State Police, and I'm sure it helped my licensing go quicker. I received my temp license 2 weeks ago and my permanent one was posted online this week.
Anyway, hope this helped! Good luck!