Illinois Tax Residency Rules

Illinois State Tax Residency Overview

Whether an individual is a resident of Illinois for income tax purposes significantly affects their tax liability. An Illinois resident is generally subject to Illinois income tax on worldwide income, whereas a nonresident is taxed only on income derived from Illinois sources — wages earned in Illinois, income from Illinois businesses, and gains from Illinois real property.

Illinois imposes a flat individual income tax rate of 4.95% on net income, a rate established by the Illinois Income Tax Act and mandated to be uniform under Article IX, Section 3(a) of the Illinois Constitution. Unlike states such as New York or Massachusetts, Illinois does not impose a progressive surtax on high earners at the state level. However, Illinois also imposes a state estate tax with a $4 million exemption — and because that threshold is not indexed for inflation, it has grown increasingly significant for affluent Illinois residents over time.

Illinois applies a two-part residency test: the domicile test and the statutory residency test. An individual is an Illinois resident for income tax purposes if they meet either test during the taxable year. See 35 ILCS 5/1501(a)(20).

Domicile Test

If your domicile is Illinois, you are an Illinois resident for income tax purposes. Your domicile is your permanent and primary home — the place you intend to return to after any absence, whether for work, travel, or any other reason. You can maintain multiple residences — a Chicago condominium, a lake house, a vacation home — but you can have only one domicile at any given time.

Your Illinois domicile does not change simply because you acquire property in another state, spend extended time elsewhere, or take steps that superficially suggest a new home base. It changes only when you physically move to a new location and form the genuine intent to make that new location your permanent home. The Illinois Department of Revenue ("IDOR") evaluates all aspects of an individual's life — where they work, where their family lives, where they maintain social and business ties, where they keep their most important possessions — to determine whether a true change of domicile has occurred.

Factors Considered in Domicile Determinations

IDOR examines the totality of an individual's circumstances when auditing a claimed change of domicile. Relevant factors include:

• Location of the primary residence and disposition of the former Illinois home (sold, rented, or retained);
• Where the individual is registered to vote and actually votes;
• State of issuance of driver's license and motor vehicle registrations;
• Location of bank accounts, particularly the primary checking account;
• Location of the individual's physicians, dentists, attorneys, and other professional advisors;
• Location of business activities and employment;
• Where the individual's spouse, children, and other immediate family members reside;
• Location of social, fraternal, country club, and religious memberships;
• Location of the individual's most valued or sentimental personal property;
• Address used for mail, financial accounts, and insurance policies; and
• Percentage of time physically present in Illinois versus the new claimed domicile.

No single factor is determinative. Domicile is determined based on the weight of all evidence considered together. A person who claims Florida domicile but retains a Lincoln Park penthouse, sends children to a Chicago private school, belongs to a North Shore country club, and sees Chicago-based physicians will face a difficult audit regardless of where they are registered to vote.

Statutory Residency Test

Even if your domicile is outside Illinois, you are treated as an Illinois resident for a tax year if both of the following conditions are satisfied:

• You maintained a permanent place of abode in Illinois during the taxable year; and
• You spent more than 183 days in Illinois during the taxable year.

Both conditions must be met. A non-domiciliary who maintains an Illinois apartment but spends only 140 days in Illinois is not a statutory resident. Equally, a non-domiciliary who spends 200 days in Illinois but has no permanent place of abode there — staying solely in hotels or with friends — is generally not a statutory resident. When both conditions are met, the individual is taxed on worldwide income as an Illinois resident for that year. See 35 ILCS 5/1501(a)(20); 86 Ill. Admin. Code § 100.3020.

The 183-day threshold means that spending exactly 183 days in Illinois keeps you a nonresident; 184 or more days in Illinois during the calendar year — combined with a permanent place of abode — triggers statutory resident status.

Permanent Place of Abode

A "permanent place of abode" is a dwelling that the individual maintains on a permanent rather than temporary or transient basis. The key considerations are whether the dwelling is suitable for year-round habitation and whether the individual has ongoing access to it and treats it as a regular place of lodging. Ownership is not required — a leased apartment qualifies. IDOR regulations also include a dwelling maintained by the individual's spouse.

The following are generally not considered permanent places of abode:

• A seasonal vacation property used only briefly and not maintained for year-round use;
• A hotel room or corporate apartment used only during short business visits; and
• A dwelling that the individual has made available exclusively to others and does not personally use.

Whether a particular property qualifies is a facts-and-circumstances inquiry. A Chicago condominium that the taxpayer keeps furnished, stores personal belongings in, and uses during regular visits is highly likely to constitute a permanent place of abode — even if the taxpayer claims a primary residence elsewhere.

Illinois Estate Tax

Illinois imposes a separate state estate tax on the estates of Illinois residents. The exemption amount is $4 million per individual — a threshold that, unlike the federal estate tax exemption, is not indexed for inflation. As a result, the Illinois estate tax captures a growing share of Illinois estates over time as asset values rise.

Illinois estate tax rates are graduated, beginning at 0.8% and reaching 16% on amounts above approximately $10 million. There is no separate state gift tax in Illinois, but lifetime taxable gifts made within three years of death may be included in the Illinois gross estate for tax purposes.

For an Illinois resident with a taxable estate of $10 million, the Illinois estate tax — after applying the $4 million exemption — can approach $1 million, with a blended effective rate well below the 16% top rate due to the graduated schedule. For estates in the $20–$50 million range, the Illinois estate tax liability can reach several million dollars. By contrast, states such as Florida and Texas impose no state estate tax whatsoever. This differential has made Illinois estate tax planning — including changing domicile before death — a significant consideration for affluent Illinois residents and their advisors.

While proposals have been introduced in the Illinois General Assembly to increase the exemption, current law remains at $4 million. Notably, HB2601, introduced in February 2025 by Rep. Adam Niemerg, would increase the exclusion to $8 million for persons dying on or after January 1, 2026. As of the date of this article, HB2601 has not been enacted and the $4 million exemption remains in effect. Importantly, unlike federal law, Illinois provides no portability of the estate tax exemption between spouses — each spouse's exemption must be used or lost at death, making estate planning for married Illinois residents more complex than under federal rules.

The Illinois estate tax applies based on the decedent's domicile at the time of death, not based on time spent in the state. Accordingly, a successful change of domicile from Illinois can eliminate Illinois estate tax exposure entirely, while an unsuccessful change — one that IDOR challenges and wins — means the full Illinois estate tax applies. See 35 ILCS 405/1 et seq.

Counting Days in Illinois

For purposes of the statutory residency test, any part of a day spent in Illinois counts as a full day in Illinois. You do not need to be present at your permanent place of abode for the day to count — presence anywhere in Illinois suffices. Arriving in Chicago late at night and departing the following morning constitutes two days in Illinois.

Days spent in Illinois solely for the purpose of boarding a connecting flight or passing through the state in transit to a destination outside Illinois may be disregarded in limited circumstances. However, the burden of establishing the travel-day exception falls on the taxpayer, and contemporaneous documentation is required.

Burden of Proof and Record Keeping

The burden of proof in an Illinois residency audit falls on the taxpayer. Any individual domiciled outside Illinois who maintains a permanent place of abode in Illinois and claims nonresident status must be prepared to substantiate that they spent no more than 183 days in Illinois during the taxable year.

IDOR auditors are methodical. In practice, auditors request or subpoena:

• Cell phone carrier records showing towers and locations throughout the year;
• Credit card and bank statements showing point-of-purchase locations;
• I-PASS, Illinois Tollway, and other electronic toll records;
• Airline frequent flyer statements and boarding passes;
• Medical and dental appointment records;
• Club, gym, and country club check-in records; and
• Social media posts, photos, and location check-ins.

Contemporaneous records — kept day by day as events occur — carry substantially more weight than reconstructed calendars prepared after an audit begins. Tax tribunals have repeatedly found reconstructed records, unsworn statements, and calendars with unexplained gaps insufficient to meet the taxpayer's burden.

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Part-Year Residents

An individual who moves into or out of Illinois during the taxable year is generally treated as a part-year resident. A part-year resident is taxed as an Illinois resident for the portion of the year during which they were domiciled in Illinois, and as a nonresident for the remainder. Illinois uses a proration method to allocate income between the resident and nonresident periods, reported on Schedule NR of the Illinois Form IL-1040. Individuals changing their Illinois domicile mid-year must document the precise date of domicile change, as that date determines which income is subject to Illinois worldwide taxation and, critically, which year's estate may be subject to the Illinois estate tax in the event of death.

Conclusion

Illinois's combination of a 4.95% flat income tax, a state estate tax with a $4 million non-inflation-adjusted exemption, and an active IDOR audit program makes residency status a consequential tax planning decision for high-income and high-net-worth individuals with Illinois ties. The domicile rules are strict, the estate tax exposure is real, and IDOR has proven willing to challenge claimed changes of domicile — particularly among departing Chicago-area residents with ongoing ties to the state.

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