Depends. I have lived in IL for 20 years and never attached the federal return, and was never asked for it in the years we were due a refund. However, in 2019, I did not include it, when I apparently should have, based upon our circumstances (i.e., a difference between W-2 wages and adjusted gross income). After providing the federal return via mail in May, 2019, (electronic submission after the fact is not an option), we finally received our refund in January, 2020.
