750 ILCS 36/203: Jurisdiction To Modify Determination.

Except as otherwise provided in Section 204, a court of this State may not modify a child-custody determination made by a court of another state unless a court of this State has jurisdiction to make an initial determination under Section 201(a)(1) or (2) and:

(1) the court of the other state determines it no longer has exclusive, continuing jurisdiction under Section 202 or that a court of this State would be a more convenient forum under Section 207; or

(2) a court of this State or a court of the other state determines that the child, the child's parents, and any person acting as a parent do not presently reside in the other state.