I work remotely for a California company (1099-NEC) and live in Illinois. How do I file my state tax?

You will file an Illinois resident return and may have to file a California nonresident return.

 

California says: "If the nonresident performs services from her or his home state, and the benefit is received in California, an independent contractor operating as a sole proprietor will have California source income under California Code of Regulations (CCR), title 18, Section 17951-4(c), when the business is unitary."

 

We'd have to know more about what you do for the California company.

 

Illinois requires residents to file state returns using the same filing status as federal. If you are filing together for federal you would file together for IL.

 

No tax is withheld on a Form 1099-NEC. In the future consider making quarterly estimated tax payments so you won't owe so much when you file.

 

Market-based sourcing for independent contractors

Also keep in mind, that while it may appear you are taxed twice on your CA income, you will receive a credit for taxes paid to other states on your IL return.

This minimizes the "double tax" impact.

Prepare your CA return first as you will need this information when preparing your IL return.

Thanks@ErnieS0.

 

I don't think I am a sole proprietor but not entirely sure. I don't own a business and my employer hires me as an independent contractor instead of as an employee. In this case, Do I still need to pay California state tax?

The IRS considers you to be a sole proprietor, a business if you are hired as an independent contractor. 

 

 To add you 1099-NEC as an independent contractor on Schedule C follow these steps:

1. Open or continue your return
2. Search for schedule c and click the Jump to link in the search results
3. Answer Yes to Did you have any self-employment income or expenses?
   • If you've already entered self-employment work and need to enter more, select Add another line of work
4. Follow the onscreen instructions

Yes, you may still need to file a Nonresident California tax return.  "As a nonresident, you pay tax on your taxable income from California sources..." Ref: California Franchise Tax Board.

 

If you need to pay California state tax it depends on your income and where it was earned.  This link; California Franchise Tax Board has the California filing requirements based on residency and income.

@melindacy