A .357 is minimal for IL deer. You really wouldn't want to go less in caliber or power level. .41 and .44 will do the trick.why so much gun for a skinny deer? A good 180gr .357 mag would do the job without putting quite as much a dent in the web of your hand or the folds of your wallet.
If a person hasn't seen IL deer then they don't realize their size. According to Buckmasters the next trophy whitetail will come out of west central IL. Every year there are deer taken that come close to the record. We're talking some big deer. Field dressed at 300+ lbs isn't uncommon in the "Golden Triangle" of west central IL. They're good corn fed deer.
Here are some pictures from previous years.