750 ILCS 22/609

Procedure to register child-support order of another state for modification. A party or support enforcement agency seeking to modify, or to modify and enforce, a child-support order issued in another state shall register that order in this State in the same manner provided in Sections 601 through 608 if the order has not been registered. A petition for modification may be filed at the same time as a request for registration, or later. The pleading must specify the grounds for modification.