Illinois Tax Residency (temporary or transitory purpose)

Key parameters
Presence	More days than any other state
Period / Window	Tax year (1 Jan – 31 Dec)
Counting	Any part of a day
Alternative	Domicile
Additional requirements	Purpose of the stay decides

This applies to anyone spending substantial time in Illinois, and to anyone who has been an Illinois resident and is trying to stop being one. You are a resident if either of these applies:

• Present for other than a temporary or transitory purpose — your reason for being in the state is open-ended rather than a short stay with a defined end.
• Domiciled in Illinois but away temporarily — your settled home remains Illinois and your absence has a limited purpose.

Days do appear, but only through rebuttable presumptions. Someone who was an Illinois resident in one year is presumed resident the next if they spent more days in Illinois than in any other state. Claiming an Illinois homestead property exemption raises the same presumption. Both can be overcome, but only by clear and convincing evidence.

So the absence of a threshold does not mean you can stop counting. It means you count differently: not against a limit, but as a running comparison between Illinois and every other state you spend time in. That matters most for people who move between states often, where no single state takes an obvious majority and the largest share can change late in the year.

• No day count protects you. Because there is no threshold, spending well under half the year in Illinois does not by itself make you a nonresident.
• The presumption is comparative, not absolute. Spending 100 days in Illinois and 90 in every other state separately can be enough to raise it.
• A homestead exemption raises a presumption on its own. Claiming the Illinois property exemption presumes residence regardless of where you spent the year.
• Presumptions need clear and convincing evidence to rebut. That is a higher bar than the ordinary balance applied to most tax questions.
• Leaving requires an indefinite absence. An absence for a short and definite period does not break Illinois residence, however far away it takes you.

A resident is taxed on income from all sources while a nonresident pays only on Illinois-source income, so an error usually surfaces as out-of-state earnings never reported after a move the state does not accept was permanent. The Department charges interest from the original due date and adds penalties for filing late and for underpaying, and a presumption of residence stands until rebutted by clear and convincing evidence. Professional tax advice is strongly recommended in situations like this.

A move the state does not accept

You leave Illinois for a two-year assignment in Texas, keeping your Chicago house and returning often. The absence is for a defined period and your home remains, so Illinois residence continues despite the low day count.

The year after a departure

You moved out of Illinois last year and now split the year between Illinois, Florida and Arizona, with Illinois taking the largest single share. Having been a resident the year before, you are presumed resident again, and rebutting that needs clear and convincing evidence.

An indefinite move with ties cut

You sell your Illinois home, take an open-ended role in Colorado, register to vote there and spend only a handful of days back in Illinois. The absence is long and indefinite and no presumption attaches, so residence ends.

• Illinois Administrative Code — Title 86, Section 100.3020, resident
• Illinois Department of Revenue — Individual income tax