735 ILCS 5/3-105
Summons issued in any action to review the final administrative decision of any administrative agency shall be served by registered or certified mail on the administrative agency and on each of the other defendants except in the case of a review of a final administrative decision of the regional board of school trustees, regional superintendent of schools, or State Superintendent of Education, as the case may be, when a committee of 10 has been designated as provided in Section 7-6 of the School Code, and in such case only the administrative agency involved and each of the committee of 10 shall be served. The method of service shall be as provided in the Act governing the procedure before the administrative agency, but if no method is provided, summons shall be deemed to have been served either when a copy of the summons is personally delivered or when a copy of the decision is deposited in the United States mail, in a sealed envelope or package, with postage prepaid, addressed to the party affected by the decision at his or her last known residence or place of business. The form of the summons and the issuance of alias summons shall be according to rules of the Supreme Court. No action for administrative review shall be dismissed for lack of jurisdiction based upon the failure to serve summons on an employee, agent, or member of an administrative agency, board, committee, or government entity, acting in his or her official capacity, where the administrative agency, board, committee, or government entity has been served as provided in this Section. Service on the director or agency head, in his or her official capacity, shall be deemed service on the administrative agency, board, committee, or government entity. No action for administrative review shall be dismissed for lack of jurisdiction based upon the failure to serve summons on an administrative agency, board, committee, or government entity, acting, where the director or agency head, in his or her official capacity, has been served as provided in this Section. Service on the administrative agency shall be made by the clerk of the court by sending a copy of the summons addressed to the agency at its main office in the State. The clerk of the court shall also mail a copy of the summons to each of the other defendants, addressed to the last known place of residence or principal place of business of each such defendant. The plaintiff shall, by affidavit filed with the complaint, designate the last known address of each defendant upon whom service shall be made. The certificate of the clerk of the court that he or she has served such summons in pursuance of this Section shall be evidence that he or she has done so.
The changes to this Section made by this amendatory Act of the 95th General Assembly apply to all actions filed on or after the effective date of this amendatory Act of the 95th General Assembly.
735 ILCS 5/3-105