If your son is living and working in IL he will need to file an IL tax return. If he moved to IL sometime during the tax year, he will be filing a part-year IL return. His NY drivers license does not make him exempt from paying tax in IL. It will, however, prevent him from being able to e-file an IL tax return. IL is pretty picky about who can e-file--you cannot e-file an IL tax return unless you have an IL state ID or drivers license. So if he does not have an IL license by tax-filing time he will have to file his IL return by mail.
If your son lived in NY and earned income in NY during the tax year he will also need to prepare a part-year NY tax return.
https://ttlc.intuit.com/questions/1901227-how-do-i-file-a-part-year-state-return
https://ttlc.intuit.com/questions/1901560-how-do-i-file-if-i-moved-to-a-different-state-last-year
https://ttlc.intuit.com/questions/2895983-how-do-i-allocate-split-income-for-a-part-year-state-retur...
Further----your son should become familiar with IL state law regarding moving into IL and obtaining an IL drivers license. He has 90 days.
https://www.ilsos.gov/services/newresidentshowdoi.html
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
