Early October...you can expect anything. I've hunted IL in october in the snow, rain, wind, heat, fob, humity, etc. At this time of year....you can't predict the weather in IL for the coming October. Best bet, as the time draws near, keep checking the weather and pack as you see it.

I would pack for layers. Can always layer to be warm in the cold. Shed layers if it's warm. Don't forget rain gear.

J