I have a new client who was a full-year IL resident in 2021. He worked 128 days in TX during 2021. His 2021 W-2 is kind of strange because it shows that his wages were sourced 100% to Texas even though he was an IL resident during all 12 months of 2021. 

He filed his 2021 IL tax return showing that none of his wages were sourced to Illinois and so he paid no income tax. Today, he received a notice from the IL Dept. of Revenue indicating that he owes IL tax on his 2021 wages - notwithstanding the fact that the W-2 shows that the wages were TX-sourced.

I think the IL notice is right and that he owes the money because was an IL resident. He can claim a credit for the non-IL taxes paid (which is zero). The client disagrees with me but I think I'm right. Any support that I can provide to him as evidence that he owes 100% IL tax on those wages?