20 ILCS 1805/86
Whenever 12 or more persons, any of them armed with clubs or dangerous weapons, or 30 or more, armed or unarmed are unlawfully, riotously or tumultuously assembled, it is the duty of the commanding officer of such military force as may be present on duty, to go among the persons so assembled, or as near them as safety will permit, and in the name of the State command them immediately to disperse, and if they do not obey, every person refusing to disperse shall be deemed one of such unlawful assembly and shall be guilty of a Class A misdemeanor; and each officer having notice of such unlawful assembly and refusing or neglecting to do their duty in relation thereto, as aforesaid, shall be guilty of a petty offense.
When persons so unlawfully assembled neglect or refuse, on command, as aforesaid, to disperse, it shall be the duty of the above military authorities to forthwith suppress such assembly and disperse the persons composing it in such manner as may be most expedient.
If in the efforts made as aforesaid to suppress such assembly and to arrest and secure the persons composing it who neglect or refuse to disperse, though the number remaining be less than 12, any such persons, or any persons, present as spectators or otherwise, are killed or wounded, the military personnel, each and all of them, shall be held guiltless of any crime and justified in law.
20 ILCS 1805/86