I have had this happen to me before. I shot a doe and it died on the neighbors property. I went to their house to ask permission and was denied. Later I found out they retrieved the deer and butchered it in their garage. I don't know if they tagged it or not, but it did not go to waste in the woods. That doesn't makewhat they didright, but......
After that, I will admit, I have crossed the property line to retrieve a deer only because the owner was not home or answered the phone. So I left my information on their door stating I retrieved a deer from their property. I was contacted later by the landowner and was asked where I found it. Granted I took a chance on leaving my information and trespassing on their land, but the deer does deserve the respect.
The owner from anotherpiece of land that butts up against where I hunt is not alocal owner, so Icall him every year before the season to ask permission just in case.
I don't know what the law is here in IL but willlook into it. I only went from what I was told.