How to change child support in Illinois
The rule for changing support, the forms, and a ready letter to the agency.
Checked against official sources: Oct 25, 2026.
Short answer
To modify an order means to change the amount by a new order. Either parent or the child's guardian can ask for a change at any time. CSS reviews its cases every 3 years and, as a rule, needs about a 20% increase or decrease for a change.
- Agency review
- Every 3 years if a parent asks (federal law)
When you can ask for a change in Illinois
Either parent or the child's guardian can ask for a change at any time. CSS reviews its cases every 3 years and, as a rule, needs about a 20% increase or decrease for a change. In court, the judge decides whether there has been a substantial change in circumstances.
Law: 750 ILCS 5/510
Can I ask for a change? Check your situation
How a change is made in Illinois
Request a free CSS review by calling 1-888-245-1938, using the online modification form, or emailing the Affidavit of Income and Expenses (HFS 2782J) and the Disclosure Statement on Legal Representation (HFS 3304). You must have an open CSS case. If CSS denies your request, you can still go to court yourself.
- Affidavit of Income and Expenses (HFS 2782J)
- Disclosure Statement on Legal Representation (HFS 3304)
- HFS: Changing a child support payment amount
Write to the child support agency to ask for a review: Ask the agency to review (change) your order
New rules in Illinois
The HFS Child Support Estimator page was revised March 20, 2026; HFS says the estimator reflects 2024 state and federal income withholding levels and the 2024 federal poverty guideline for one person.
If a parent is in jail or prison
State guidelines may not treat time in jail or prison as choosing not to work, when support is set or changed.
Law: 45 CFR 302.56(c)(3)
In nearby states
Steps to change support in Illinois
Get the order
Find the date and the amount on the order.
Check the rule
In Illinois: Either parent or the child's guardian can ask for a change at any time.
Show the change
Bring proof of the change, such as pay stubs or a layoff notice.
Send your request
Contact Illinois Department of Healthcare and Family Services (HFS), Child Support Services (CSS) (1-800-447-4278) · Apply online
Talk to legal aid
Ask for free help: Illinois Legal Aid Online and Illinois State Bar Association Illinois Lawyer Finder.
Where to get free help in Illinois
Questions about changing support in Illinois
How often can I ask for a change in Illinois?
Either parent or the child's guardian can ask for a change at any time. CSS reviews its cases every 3 years and, as a rule, needs about a 20% increase or decrease for a change. In court, the judge decides whether there has been a substantial change in circumstances.
Where do I file to change support in Illinois?
Request a free CSS review by calling 1-888-245-1938, using the online modification form, or emailing the Affidavit of Income and Expenses (HFS 2782J) and the Disclosure Statement on Legal Representation (HFS 3304). You must have an open CSS case. If CSS denies your request, you can still go to court yourself.