20 ILCS 505/9.5
When the Department has determined that a parent or guardian is liable for payment for care and support of the parent's or guardian's children, the parent or guardian shall be notified by mailing the parent or guardian a copy of the determination by mail, advising the parent or guardian of the parent's or guardian's legal obligation to make payments for such period or periods of time, definite in duration or indefinite, as the circumstances required. The notice shall direct payment as provided in Section 9.6.
Within 30 days after receipt of a payment notice, the parents may appeal the assessment amount if the data used in determining the amount is inaccurate or incomplete. Parents may also appeal the assessment at any time on the basis of changes in their circumstances which render inaccurate information on which the assessment is based. If the changes requested in a parental appeal are granted, the Department may modify its assessment retroactively to the appropriate date and adjust any amount in arrears accordingly.
20 ILCS 505/9.5