I'm not from Illinois and have never hunted there even tho I have been to Rock Island for training a few times back in my working days. So telling you speifically what the deer are eating in your area is really a job for the local game biologists not us.
But in general deer are browsers and not grasers. So they eat tender new growth of all kinds. Forbs (weeds to us) are a favorite as are the new growth at the tips of most woody shrubs, vines, bushes, etc. Here they eat green briar, blackberry bushes, sumac tips, mushrooms, anything green and still growing. Things like that.
GB