If it was just discovered that, 8 years ago, someone unknowingly gave medicine to another to cure an STD - that they weren't aware they had - is it still possible to press charges in the state of Illinois?
The statute of limitations for criminal prosecution has passed in Illinois (3 years for a felony). There are some exceptions if the crime is murder, or the accused has fled the state. This is based on when the act occurred. A civil action for personal injury is also possible, which has a statute of limitations of 2 years. This is "within 2 years next after the cause of action accrued": the statute does not specify what that means. Illinois follows what is known as the "discovery rule", meaning after the injury was discovered (for example a brain injury caused by a hit on the head), specifically (Knox College v. Celotex, 88 Ill.2d 407)
when a party knows or reasonably should know both that an injury has occurred and that it was wrongfully caused, the statute begins to run and the party is under an obligation to inquire further to determine whether an actionable wrong was committed.
So the two primary question are, has an injury been suffered (probably, but not definitely), and is a lawsuit time-barred – that depends on the specifics of the case (hence consultation with an attorney is necessary).