The short answer to this question is: it depends.
Illinois law concerning fault and recovery has gone through several serious transformations. Up until the 1981 Illinois Supreme Court decision, Alvis v. Ribar, Illinois used a "contributory negligence" system to determine whether a plaintiff could recover in a personal injury claim. Alvis v. Ribar, 85 Ill. 2d 1 (Ill.1981). Under this system, any degree of fault attributable to a plaintiff was an absolute bar to recovery.
The Alvis decision ushered in a new set of laws pertaining to fault and recovery in Illinois. Under the new "comparative negligence" legal system, plaintiff recoveries were limited by the percentage of their own negligence or fault. So theoretically, if a plaintiff were 25% at fault or even 75% at fault, that plaintiff could recover with a reduction reflecting the percentage of their fault.
In 1986, the Illinois State Legislature enacted law that has supplanted Alvis's comparative negligence system. The new law is a hybrid between contributory negligence and comparative negligence. Since 1986, Illinois has been a "modified contributory negligence" state. 735 ILCS 5/1116. Under the current modified contributory negligence system, recoveries for damages are diminished in proportion to the percentage of fault attributable to the plaintiff. (Similar to comparative comparative negligence laws). However, plaintiffs who are more than 50% at fault are completely barred from recovery. (Similar to contributory negligence laws).