According to the Illinois instructions:
An Illinois resident is an individual that is domiciled in Illinois for the entire tax year.
A Nonresident of Illinois is an individual that is not domiciled in Illinois at any time during the year.
A Part-Year Resident is an individual that moved into or out of Illinois during the year.
What if my spouse and I have different residency States?
If one spouse is a resident and the other is not, you may file separate state returns. If you file a joint Illinois return, both spouses will be taxed as if they are residents.
To file a married filing separate Illinois return when filing a joint federal return, follow these steps:
- Go to the State Section
- Basic Personal Information
- Change Filing Status from MFJ to MFS for STATE purposes only
- Answer Yes to create the Married Filing Separate return
- MFS for State purposes only section
- Indicate who the Illinois return is for and complete the required information.