• you filed a federal income tax return;
• you were not required to file a federal income tax return, but your Illinois base income, Line 11, was greater than your Illinois exemption allowance on Line 12; or
• you are claimed on your parents' or another person's return and your Illinois base income, Line 11, is greater than the exemption allowance on Line 12.

If you are a part-year resident (i.e., you were a resident of Illinois for part, but not all of the year), you must file Form IL-1040, Individual Income Tax Return and Schedule NR, Nonresident and Part-Year Resident Computation of tax, if

• you earned income from any source while you were a resident,
• you earned income from Illinois sources while you were not a resident, or
• you want a refund of any Illinois Income Tax was withheld.

If you were a nonresident (you were not an Illinois resident at any time during the tax year), you must file Form IL-1040, Individual Income Tax Return and Schedule NR, Nonresident and Part-year Resident Computation of tax, if:

• you earned enough taxable income from Illinois sources to have a tax liability, or
• you want a refund of any Illinois Income Tax was withheld in error. You must attach a letter of explanation from your employer.

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