I see nothing in Illinois law that prevents a private party from disclosing to others the fact of a criminal conviction, even if the conviction is later expunged. I see language to the effect that "in response to an inquiry for expunged records, the court, the Department, or the agency receiving such inquiry, shall reply as it does in response to inquiries when no records ever existed", but a former employer doesn't fall into those categories. See 20 ILCS 2630/0.01, et seq. Are you looking at a different statute?

On the other hand, 775 ILCS 5/2-103 prohibits your prospective employer from considering an expunged conviction when making its hiring decision.