Wisconsin/Illinois Tax reciprocity

[Mshats525]

I am a full-time Wisconsin resident working in Illinois.  My employee withheld state taxes from both states in 2025.  I have since submitted an IL-W-5-NR and that has stopped.  I have completed my IL-1040 to get a full refund on the Illinois taxes withheld, however, the IL-1040 instructions indicate I need to include a letter from my employer with an explanation of why Illinois taxes were withheld in error.  My employer is not willing to write me a letter, is this really necessary??  

[BrittanyS]

Yes per the Illinois Department of Revenue, "If your employer withheld Illinois tax from your pay in error, you must attach a letter from your employer, on company letterhead, to your Form IL-1040 to verify that Illinois tax was withheld in error."  Have you explained to your employer that this is a requirement from the Illinois Department of Revenue?

See link below:

Illinois Department of Revenue