In Iowa I have been checked 2 times in six years (1 bowhunting, 1 pheaseant) and have talked to the DNR two other times while bow hunting.
However, IL is another story, I think I have been checked every year for the last 5 or 6 during deer season and twice during turkey season and I absolutely love it. Our farm and those surrounding us have been known to have been trespassed and poached on alot in previous years so we were happy to see the DNR down patrolling frequently. Even when he hasn't checked us I know he is hangin out alot because he can usually tell me many days that we hunted in the previous weeks (based on our vehicles being in the fields). Kinda makes a guy feel good about the patrol around his property.
I also agree with the others, post the TIP signs on your property so those around you have easy access to the number, keep the TIP and DNR numbers readily available and do some self patrolling if you can.
I have to add one more DNR story that I thought was unbelievable this year. We were hunting the shotgun opener in IL and the DNR showed up about 9:30 opening morning, pulls 300 yards into our field, gets out of the car and checks the ATV (no big deal). He then proceeds to walk over to the neighbors fence, jump it, walk to the neighbors Condo (eleveated blind), walk up the ladder and step inside to check him out, thought that was a bit extreme but ok. Then he crossed back over the fence walks down our field edge spotting all of us with his binos and jumps back in his truck and leaves. Now none of this was really a big deal, except we were in the middle of a hunt, but hey at least he is doing his job. The only thing that got me was that he walked several hundred yards to check out the neighbor and down our field edge with no orange on!!! Maybe a mental lapse, but I wouldn't be caught out there with orange on during the gun season, even if I was a DNR officer