A common misconseption in IL is that you have to have permission to enter upon a private property. True in the instance of a building but not land. Unless you have been told prior to entering upon that property that you are not welcome it is open game. One way to get around that is to post your ground clearly from all sides.

(720 ILCS 5/21‑3) (from Ch. 38, par. 21‑3)
Sec. 21‑3. Criminal trespass to real property.
(a) Except as provided in subsection (a‑5), whoever:
(1) knowingly and without lawful authority enters or

remains within or on a building; or
(2) enters upon the land of another, after receiving,

prior to such entry, notice from the owner or occupant that such entry is forbidden; or
(3) remains upon the land of another, after receiving

notice from the owner or occupant to depart; or
(3.5) presents false documents or falsely represents

his or her identity orally to the owner or occupant of a building or land in order to obtain permission from the owner or occupant to enter or remain in the building or on the land;
[/align]commits a Class B misdemeanor.
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