Individual states promulgate laws to comply with the federal law — The Personal Responsibility and Work Opportunity Reconciliation Act of 1996. This act is codified at 42 USC 653-653A. Employers need to only comply with state laws.
Illinois 820 ILCS 405/1801.1 requires employers to report not later than 20 days after the date the employer hires the employee or, in the case of an employer transmitting reports magnetically or electronically, by two monthly transmissions, if necessary, not less than 12 days nor more than 16 days apart.
Contact
Employee Benefits Security Administration (EBSA), Office of the Assistant Secretary
Regulations
29 CFR chapter XXV (Parts 2509 – 2590)