There are few restaurants in Champaign-Urbana that are open 24 hours. There are the Merry Ann's/Merry-Ann's/Mary Anne's diners, but you don't feel super comfortable there with grease in the air. I love Merry Ann's diner food, but Perkin's just feels homier.
I've gone to Perkins in the middle of the night to get work done; order a snack and bottomless coffee. It's quiet, the booths are cushy, and there's pie if you need some sugar for energy.