Illinois Statutes Chapter 215. Insurance § 5/121-7. Service of Process--Notice

(a) Notice of such service and a copy of the court process or the notice, order, pleading, or process in such administrative proceeding are sent within 10 days thereafter by certified mail by the plaintiff or the plaintiff's attorney in the court proceeding, or by the Director of Insurance in the administrative proceeding, to the defendant in the court proceeding or to whom the notice, order, pleading, or process in such administrative proceeding is addressed or directed at the last known principal place of business of the defendant in the court or administrative proceeding.

(b) The defendant's receipt or receipts issued by the post office with which the letter is registered, showing the name of the sender of the letter and the name and address of the person or insurer to whom the letter is addressed, and an affidavit of the plaintiff or the plaintiff's attorney in a court proceeding or of the Director in an administrative proceeding, showing compliance therewith are filed with the clerk of the court in which such action, suit, or proceeding is pending or with the Director in administrative proceedings, by the date the defendant in the court or administrative proceeding is required to appear or respond thereto, or within such further time as the court or Director, as the case may be, may allow.