If my employer has multiple offices in different states, and I have worked between both, do I need to file both state taxes or just my resident state?

[awofox]

It is my current situation that I work in an Illinois based office for an Illinois based company, but I live in Missouri and have also worked several months throughout 2017 at the Missouri branch.

My W-2 only shows Missouri Tax withholding with a Missouri Employer ID, nothing about Illinois.

I should also mention I started work in Missouri before my company transferred me to the Illinois branch.

I realize there is no reciprocity between Illinois and Missouri, and this situation is a bit bizzare, but do I have income tax liability in Illinois?  And if so, would I have to try and split my reported income over the year between the two offices?

[TomD8 · Accepted solution]

Illinois (like other states) taxes non-residents on income earned from physically working within its borders.  Therefore you do have to file a non-resident return in IL in addition to your home state return in MO.  MO can tax ALL your income, including your earnings from IL, but you'll be able to take a credit on your MO return for the taxes paid to IL, so you won't be double-taxed.

This FAQ explains how to do a non-resident state return in TurboTax:  https://ttlc.intuit.com/questions/1901271-how-do-i-file-a-nonresident-state-return

Note that you should complete the non-resident state return BEFORE you do your home state return.