Like other states, Illinois taxes its residents on all their income, regardless of where earned. Additionally, California can tax you as a non-resident on income from work performed in California. So you have to file both a non-resident CA tax return and a resident IL tax return.
IL will give you credit for the tax paid to CA, so you won't be double-taxed. In TurboTax, complete the non-resident state return before the home state return, so that the program can calculate and apply the credit.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
