65 ILCS 5/11-13-8
In municipalities of 500,000 or more population, when any zoning ordinance, rule or regulation is sought to be declared invalid by means of a declaratory judgment proceeding, not more than 30 days before filing suit for a declaratory judgment the person filing such suit shall serve written notice in the form and manner and to all property owners as is required of applicants for variation in Section 11-13-7, and shall furnish to the clerk of the court in which the declaratory judgment suit is filed, and at the time of filing such suit, the list of property owners, the written certificate and such other information as is required in Section 11-13-7 to be furnished to the board of appeals by an applicant for variation. A property owner entitled to notice who shows that his property will be substantially affected by the outcome of the declaratory judgment proceeding may enter his appearance in the proceeding, and if he does so he shall have the rights of a party. The property owner shall not, however, need to prove any specific, special, or unique damages to himself or his property or any adverse effect upon his property from the declaratory judgment proceeding.
65 ILCS 5/11-13-8