@ Kat and @ finch13
While the image above that Kat provided from her Bing search may be "an" address for the Illinois DOR, I believe that may be one of several smaller branch/regional offices around the state, and may not be a return processing center, and may not be an address they want to receive returns delivered from Germany by UPS, which is what finch13 is wanting to do. And in any case they might have to then send it somewhere else for processing.
IMO, if it were me, I'd simply ask Illinois DOR outright what address they specifically want him/her to use for private delivery services like UPS and hear it "right from the horse's mouth." The IDOR questions/comment form I provided info for in the other thread would let him do that.
https://ttlc.intuit.com/community/state-taxes/discussion/re-i-go-to-ups-to-send-this-to-have-it-trac...
