It is a legal deadline to file a lawsuit. It must be met or the injury claim is barred.
Generally, in Illinois, in a personal injury case, the statute of limitations is two years for adults. It is only one year for claims against a government agency or a tavern. It is a longer period for minors. There are special rules based on when misconduct is first discovered which could extend the deadline beyond two years. An experienced lawyer can determine what statute of limitations applies in any given case.