Should I file an income tax return if I live in Illinois but work in another state?
Yes. As an Illinois resident you are subject to tax on all income no matter where it is earned. If you were taxed by another state on income you received while you were an Illinois resident, you may be entitled to a credit for tax paid to other states. See the Schedule CR instructions and Publication 111, Illinois Schedule CR for Individuals, to see if you are eligible to take this credit.