Despite the frustration of the situation, you are not allowed to physically remove trespassers. You must first give them notice, then call the police, who now can legally remove them if they fail to leave. That notice can be in verbal or written form, so the best way to keep trespassers off your property is to post clearly visible “no trespassing” signs where any potential trespassers will see them. Indicate intention to litigate to the fullest extent allowable.
Under the Illinois Criminal Code, trespass is misdemeanor that can get you 30 days to 6 months in jail, and a maximum $500 fine.
(720 ILCS 5/21-3) (from Ch. 38, par. 21-3)
Sec. 21-3. Criminal trespass to real property.
(a) A person commits criminal trespass to real property when he or she:
(1) knowingly and without lawful authority enters or remains within or on a building;
(2) enters upon the land of another, after receiving, prior to the entry, notice from the owner or occupant that the entry is forbidden;
(3) remains upon the land of another, after receiving notice from the owner or occupant to depart;
Illinois Statutes and Elements of the Crime
Criminal trespass to real property: 720 ILCS 5/21-3
Criminal trespass to a residence : 720 ILCS 5/19-4
Criminal trespass to vehicles: 720 ILCS 5/21-2
sources;
https://www.findlaw.com/state/illinois-law/illinois-criminal-trespass-laws.html
https://www.ilga.gov/legislation/ilcs/fulltext.asp?DocName=072000050K21-3