The IRS is not concerned with your state tax owed. The IRS is only concerned about your federal tax. The state is concerned though, so you need to check your records and see if you paid. Your proof that you paid your state tax will be in your own bank or credit card records. It is pretty odd that you are just now hearing from the state about tax owed from all the way back to 2016. You might be getting a letter that is a scam. Contact the state of IL and see if they really sent you a letter asking for payment for 2016.
https://ttlc.intuit.com/community/state-taxes/help/how-do-i-contact-my-state-department-of-revenue/0...
**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.**
