Ill. Admin. Code tit. 92, § 3000.1050 – Service

a) Each order, notice, or other document required to be served under this Part shall be served personally or by registered or certified mail, except as otherwise provided.
b) Service upon a person's duly authorized representative constitutes service upon that person.
c) Service by registered or certified mail is complete upon mailing. An official United States Postal Service receipt from the registered or certified mailing constitutes prima facie evidence of service.
(Recodified from 92 Ill. Adm. Code 107 (Department of Transportation) pursuant to P.A. 104-0025, at 49 Ill. Reg. 12509)