Illinois State Income Tax Overview

Illinois is one of the many states that requires the filing of state income tax by those who earn Illinois-based income.  Even though you file a state income tax return in Illinois, you still are responsible for filing a federal income tax return as well.

Following is general information about filing state income taxes in Illinois.


Who Has to File?

Residents of Illinois

If you are a resident of Illinois, you have to file state income taxes if you filed a federal income tax return or your Illinois income is greater than your Illinois exemption.  Even if you work in another state for the entire year but you reside in Illinois, you still have to file state income taxes in Illinois.

When you are filing state income taxes, you need to consider all of your income from all sources, even those outside of the state of Illinois.

Part-Time Residents of Illinois

If you lived in Illinois for only part of the tax year, you must file state income tax in Illinois if one or more of the following are true:

  • You earned income from any source while you were a resident of Illinois
  • You earned income from a source in Illinois while you lived outside of Illinois
  • You are seeking a refund of any income tax withheld by Illinois

Residents of Other States

If you live in another state but work in Illinois during the tax year, you may have to file a state income tax return in Illinois.  You have to file if you have a tax liability in Illinois (when your taxable income for Illinois is greater than your tax exemption on Illinois income) or you are seeking a refund of any Illinois income tax withheld.

What is the Tax Rate?

Starting in 2011, Illinois state income tax is a flat 5% on all income.  Tax is computed based on the taxpayer’s adjusted gross income amount calculated for federal income tax purposes plus any additional Illinois state income based on Illinois tax law.

What Date Do I Have To File By?

The date when you have to file state income taxes for Illinois is typically the same date when your federal income tax return is due.  For the 2011 tax year, state income taxes are due by April 17, 2012.

You can obtain an extension to the filing date of six months, but if you owe taxes, you must still pay them by April 17 in order to avoid any penalties or interest on the amount due.

How Do You File?

Illinois state income tax can be filed by mail or through Illinois’ e-file system.  If you owe state income tax, you can make payments of tax owned by credit card, using online transfer from a checking or savings account, or by mailing using a check.

Tax Attorney Help

The information above about Illinois state income tax is general in nature and should not be relied upon for making decision related to Illinois state income tax.  If you have questions about or need assistance preparing your Illinois state income tax return, you should speak with a tax attorney who is familiar specifically with Illinois tax laws.

by Mark Johnston

Mark has been a contributor to legal web sites related to bankruptcy, tax, and criminal law since 2011. He has an Accounting degree from Texas A&M University.