Legal Question in Civil Litigation in Illinois

You'd have to know which court(s). The defendant could have been sued in multiple places and they are not all available on one database yet. There are on-line services that say, for a fee, they can locate cases in different courts, but I can't vouch for them. I guess the question is what good would the information do for you? If you're already in a lawsuit, you may have the legal right to ask the defendant these kinds of questions through "discovery" or at trial, if they are relevant to the case. If you're suing pro se, the judge may or may not be helpful, but you're taking a risk you may not get the information you seem to think you need if you don't do it correctly by the book. Good luck.