What Is the Illinois 183-Day Rule for Tax Residency?

While many states use a 183-day rule to determine tax residency, Illinois law uses a different standard based on physical presence. If an individual spends a significant amount of time in Illinois during a calendar year, the state’s tax authorities may consider them a resident for tax purposes. This is one of several factors used to assess residency and identify individuals with enough connection to the state to be subject to its income tax.

Defining Illinois Tax Residency

Illinois tax law distinguishes between “residency” and “domicile.” Domicile is the place an individual considers their true, fixed, and permanent home. A person can have only one domicile at any given time, and it continues until they move to a new location with the clear intention of making that new place their permanent home. An individual can be considered a resident of Illinois for tax purposes even if their domicile is in another state.

Under Illinois law, a person is considered a resident if they are in the state for other than a temporary or transitory purpose. There is a presumption that an individual is a resident of Illinois if they spend more than nine months of the taxable year in the state. This means the Illinois Department of Revenue will presume residency, but the taxpayer can overcome this by providing evidence that their domicile is elsewhere.

This results in three filing statuses. A “Resident” is someone domiciled in Illinois for the year or who is present in the state for other than a temporary or transitory purpose. A “Nonresident” is an individual not domiciled in Illinois and in the state for a temporary purpose. A “Part-Year Resident” is someone who establishes or moves their domicile out of Illinois during the tax year.

Applying the Day Count

Any portion of a day that an individual is physically present in Illinois is counted as a full day. This includes days of arrival and departure. For example, arriving in Illinois late on a Friday evening and leaving early Saturday morning would be counted as two full days.

This strict counting method requires careful tracking for individuals who frequently travel to the state. The only common exception to this rule involves time spent at an airport for a connecting flight. If a person is merely transiting through an Illinois airport on their way to another destination and does not leave the airport, that time does not count as a day spent in the state.

Maintaining precise records of travel is a necessary practice for anyone whose time in Illinois approaches the nine-month presumption threshold. These records become the primary evidence to substantiate a claim of non-residency if questioned by state tax authorities. The burden of proof rests on the taxpayer to demonstrate they were not in the state for an extended period.

Documentation to Support Non-Residency

For individuals who spend significant time in Illinois but maintain a domicile elsewhere, assembling strong documentation is a preparatory step to defend their non-resident status. If a taxpayer’s presence in the state leads to a presumption of residency, the burden of proof shifts to the individual to demonstrate their permanent home is in another state. This evidence must show clear and continuing ties to the claimed state of domicile.

Key documents include:

• A current driver’s license or state identification card issued by the other state
• A voter registration card from that state
• Property tax bills for a permanent home owned outside of Illinois
• Utility bills for that residence
• Bank statements showing a pattern of transactions in the claimed home state
• Vehicle registrations, professional licenses, or memberships in organizations in the other state

Each document contributes to a comprehensive picture of the individual’s life centered outside of Illinois.

Illinois Tax Filing Requirements by Status

An individual’s determined residency status directly dictates their tax filing obligations in Illinois. The requirements differ significantly for residents, nonresidents, and part-year residents, impacting what income is taxed and which forms must be filed.

Full-year residents are subject to Illinois income tax on all of their income, regardless of where it was earned. This includes wages, investment income, and business profits from any source, inside or outside of Illinois. These individuals must file Form IL-1040, the Illinois Individual Income Tax Return, to report their worldwide income.

Nonresidents have a more limited tax obligation. They are only taxed on income earned from Illinois sources. This includes wages for services performed in Illinois, rental income from property located in the state, or profits from a business operating in Illinois. Nonresidents must also file Form IL-1040, but they must attach Schedule NR, “Nonresident and Part-Year Resident Computation of Illinois Tax,” to allocate their income.

Part-year residents face a hybrid tax situation. For the portion of the year they were considered an Illinois resident, they are taxed on all income from all sources. For the portion of the year they were a nonresident, they are taxed only on income from Illinois sources. Like nonresidents, part-year residents must file Form IL-1040 with the accompanying Schedule NR to properly separate and report their income.