Illinois doesn't tax nonresident remote workers, as long as they don't physically work there. Since you are telecommuting, the Illinois-sourced income would be $0, and it is fully taxable to CA as normal.
Here is how to complete your Illinois tax return to obtain a refund:
1. In My Info, select Other State income and choose Illinois
2. Next, go to Your State Return, choose Illinois
3 Answer Yes to Did you make money in Illinois in 2024, but never live there?
4. When you get to the screen Tell us about your Illinois Income, TurboTax will generate the amount allocated from your W-2, but you need to manually type in "0" in the box asking how much you made while working in Illinois. This will allow you to get the tax refunded.
Then, compute your California tax return as normal, and make sure all of your wages are allocated to CA.
If your employer isn't withholding CA taxes, you should make quarterly estimated payments to avoid underpayment penalty and interest. You will do this using Form 540-ES or online at the Franchise Tax Board's website.
You can advise your employer to stop withholding IL tax, by providing them Form IL-W-5-NR, Employee's Statement of Nonresidence in Illinois.
@gracenavalta [Edited 1/22/25 8:43 AM PST]
