Bobcats and cougars are very secretive animals. I've had good hunting property up in northern Michigan since 1973 where there are bobcats and I've never seen one. The closest I've been to even knowing one was around was when I found a doe that had been shot and lost by an archer and it died on my place. A cat had found it, eaten some, and then partially cover it with field debris. I have no doubt that there are bobcats in some areas of IL and probably the further south you go out of the more open agricultural areas the better chance there would probably be of them inhabiting the area.