(720 ILCS 5/) Criminal Code of 1961 Section 7. Justifiable use of force. Use of deadly force justified if the person reasonably believes they are in danger of death or great physical harm. Use of deadly force justified if the unlawful entry is violent, or the person believes the attacker will commit a felony upon gaining entry. Section 7-2(b). Prevents the aggressor from filing any claim against the defender unless the use of force involved "willful or wanton misconduct". Illinois has no requirement of retreat. (People v. Bush, 111 N.E.2d 326 Ill. 1953).
That said, the lack of CCW and the bullshit FOID are another story all together...
"The chain which can be yanked is not the eternal chain." -- G. Fitch