I am no longer a felon; I can again legally possess all of the guns and ammo that I own.
My FOID was set to expire on June 1 so I wanted to get my renewal processed early. On Monday, April 2, I processed the form and photo at GAT Guns; they said they would mail it with the others at the end of the week. Let us be charitable and assume that the Illinois State Police did not receive that bundle of mail until Monday, April 16; it took them over two months to process and mail my renewal.
If my experience is typical, you can expect a wait of bit over eight weeks for your FOID to arrive.