My question involves personal property located in the State of: Illinois

I bought a home 15 months ago. At the time of closing the previous owner stated verbally that anything left on the property was mine. An RV was parked on my lot. Two weeks later, the ex-owner's son contacted me and said that the RV was titled to him and that Mom had no right to give it away. I told him to take it away. He did not. I've called him twice, he said he would get it as soon as he could get the money to hire a truck to pull it away. The last time I told him that he had 30 days or the RV would be considered mine. The RV is still there.

What do I need to do to legally give him a deadline so that the RV will be mine if he does not get it off my land?