Error code IL1040-11870-1 is a common rejection code from the Illinois Department of Revenue (IDOR) indicating that your state return couldn't be e-filed because the information used to verify your identity or previous year's data does not match their records. This rejection usually relates to discrepancies in the Adjusted Gross Income (AGI) from the prior year or errors in personal identification information (Driver's License/State ID).
- Verify Prior Year AGI: Ensure you are using the exact AGI from your original 2024 Illinois return, not an amended one. If you did not file in Illinois last year, use 0.
- Check Driver's License/State ID: Double-check the Illinois Driver's License or State ID number and expiration date entered for you and your spouse (if filing jointly).
- Update Software: If using tax TurboTax Desktop, update it to the latest version, as this often fixes known state electronic filing bugs.
- Try Zero for AGI: If you filed late or amended your previous return, your correct AGI might not be in the system. Some taxpayers have had success entering 0.
- Paper File: If the return continues to reject, you may need to print and mail your Illinois return.