Can I e-file a prior year Illinois 1040 return?
Yes, the IL Department of Revenue indicates that they will process current year and two prior years of IL-1040 return through the Modernized e-File program.
For the 2023 filing season, 2023, 2022, and 2021 IL-1040 returns can be processed through the e-file system. All other prior IL returns must be paper-filed.