If you are 100% sure that the non-custodial parent is delinquent and you know where such person is employed then you can send an Income Withholding Notice to the employer to start collecting an amount above and beyond the current support amount to be applied to what is owed
Obtain your court order and an Income Withholding Notice
After obtaining an Income Withholding Notice you need to make sure to complete the information required which will include the information from the current court order, such as the date of the order, the name of the Judge and the amount set for current support. It is important to note that all payments withheld for support by the employer must be sent to the Illinois State Disbursement Unit. You CAN NOT have the payments sent to you directly.
How much extra can you take?
Your current order may list a specific amount that can be withheld for a delinquency, this would likely be the case if there is a Uniform Order for Support. If you order does not list an amount then you can withhold an extra 20% of the combined amount ordered for current support and any amount for payment on an arrearage. To see definitions of arrearage and delinquency read state law 750 ILCS 28/15, http://www.ilga.gov/legislation/ilcs/documents/075000280K15.htm
Contacting and serving the employer
Many employers will have a payroll or human resource department that you can call and ask where child support Income Withholding Notices can be mailed to. Most companies refer to such notices as garnishments. You need to send the Income Withholding Notice to this address, I suggest using certified mail return receipt so that you can enforce the statutory penalties if the employer fails to comply. Additionally you are not required to send a copy of the court order, only the Income Withholding Notice.
Court to be informed
Regardless of whether the certified mail is accepted or not you are required to file with the clerk of the courthouse where your case is located a copy of the Income Withholding Notice you served on the employer. You do not need to set a court date.
Waiting for the money
Assuming the employer receives the Income Withholding Notice the employer can wait 14 days before they take any action. However a withholding must occur within the current pay cycle after day 14. Thus if an employer pays once a month on the 15th and your notice is received after the 1st of the month the employer could wait to withhold until the 15th of the following month. Once the withholding occurs the employer then has 11 days to either have proof the payment was made or if no proof then that such payment was received by the Illinois State Disbursement Unit. Once received by the SDU you should have your funds within 2-3 business days.