IL - Individual Prior Year E-File

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 2020 filing season, 2020, 2019, and 2018 IL-1040 returns can be processed through the e-file system. All other prior IL returns must be paper-filed.