105 ILCS 5/14-1.11
The resident district is the school district in which the parent or guardian, or both parent and guardian, of the student reside when:
In cases of divorced or separated parents, when only one parent has legal guardianship or custody, the district in which the parent having legal guardianship or custody resides is the resident district. When both parents retain legal guardianship or custody, the resident district is the district in which either parent who provides the student's primary regular fixed night-time abode resides; provided, that the election of resident district may be made only one time per school year.
When the parent has legal guardianship and lives outside of the State of Illinois, or when the individual legal guardian other than the natural parent lives outside the State of Illinois, the parent, legal guardian, or other placing agent is responsible for making arrangements to pay the Illinois school district serving the child for the educational services provided. Those service costs shall be determined in accordance with Section 14-7.01.
105 ILCS 5/14-1.11