I had a lease for an apartment in Illinois that expired in August but was staying and working in California as of June. Not sure if it matters.
even if it was your tax home, since you have no Illinois income to report, no tax filing is required. If you filed an Illinois return for the prior year, you may get an inquiry from Illinois to which you can respond you had no Illinois income. Unfortunately, there's no way to prove it. File california as a part year resident.
If Illinois was "NOT" your tax home, then you have nothing to report to that state.
even if it was your tax home, since you have no Illinois income to report, no tax filing is required. If you filed an Illinois return for the prior year, you may get an inquiry from Illinois to which you can respond you had no Illinois income. Unfortunately, there's no way to prove it. File california as a part year resident.