Legal Question in Real Estate Law in Illinois

You don't want to screw this up. Why not have a lawyer do it the first time, so it's done "properly" and then if it happens again you can give it a try. The lawyer can review the contract and determine what form(s) would be most appropriate - among other things there may be a formal notice provision you must comply with. Because in part it depends on what you want to have happen too. Sending them a letter may or may not be formal notice under the contract but is a "friendly" reminder. If they don't respond, then you could turn up the heat. But why wouldn't a phone call save some time and then go straight to a proper notice?

Stephen gives good advice. In addition to his suggestion, if you should decide to pursue this without an attorney, make sure that all notices and letters are sent by certified mail, return receipt requested.