It all depends on what they are looking to be licensed in.
Here is Title 68 Administrative Code for Licensing:
http://www.ilga.gov/commission/jcar/admincode/068/06801130sections.html"Individual" means a person with a criminal record, who seeks a license or certificate in an occupation for which a criminal record is not expressly a per se bar, who applies to the Department for a non-binding, advisory opinion to be provided by the Board or body with the authority to issue the license or certificate as to whether his or her criminal record would bar the individual from the licensure or certification sought, should the individual meet all other licensure requirements, including, but not limited to, the successful completion of the relevant examinations [20 ILCS 2105/2105-15(i)].
You can also go to the Department of Professional Regulation for more information here, this is the site where all licenses in Illinois are obtained:
http://www.idfpr.com/