US Multistate Tax Residency and Nexus: A Practical Guide for Illinois Families and Businesses

Multistate tax residency and nexus decide which state, or states, can tax you or your business. For an individual the key words are domicile, residency and source of income; for a business they are nexus, physical presence and economic thresholds. Illinois borders Wisconsin, Indiana, Iowa, Missouri and Kentucky, and many Fox Valley residents commute or work remotely across a state line. If you or your company are connected to India or Canada, foreign income and foreign employees add federal reporting on top of the state rules. This guide covers the Illinois rules, with a checklist for other states.

Multistate tax residency and nexus: who is a resident?

Illinois treats you as a resident if you were domiciled in Illinois for the whole year. Domicile is the place where you live and intend to return after temporary absences. IDOR lists examples of temporary absences: military duty, residence in a foreign country, living out of state as a student, and winter or summer homes elsewhere. Living in Illinois only to attend school does not make a person from another state an Illinois resident.

A part-year resident moved to or from Illinois during the year. IDOR says temporary absences do not qualify you for part-year status. If you were a resident when you received income, you are taxed on 100% of it regardless of source; if you were a nonresident when you received it, you are taxed only on Illinois-source income. Many other states add a day-count test, so check each state's tax agency.

For H-1B, L-1 and TN workers renting in Aurora while keeping a home in Pune or Toronto, domicile turns on facts and intent. The federal residency tests do not decide state residency, so document your ties to each place.

Where income is sourced, and who gets credit

Wages are sourced to the state where the work is done. Illinois wages are the amount on the Illinois copy of your W-2, and a nonresident reports those. Business income earned both in and out of Illinois is apportioned with a formula. Income from Illinois partnerships and S corporations reaches nonresident owners through Schedule K-1-P.

Reciprocal agreements. An Illinois resident working in Iowa, Kentucky, Michigan or Wisconsin reports the wages in Illinois, and those states do not tax them. If an employer withheld that state's tax, you claim a refund from that state; you cannot use it as a credit on your Illinois return. A resident of one of those states working in Aurora files Form IL-W-5-NR with the employer and owes no Illinois tax on wages, though Illinois taxes other income, such as lottery winnings.

Other states. Indiana and Missouri are not on the reciprocal list. If an Aurora resident works in Indiana and Indiana taxes the wages, Illinois taxes them too, and Schedule CR gives a credit, subject to its limits. The credit requires that you filed a required return in the other state, does not cover interest or penalties, and is unavailable to nonresidents. Part-year residents take it only on income earned while resident. IDOR allows no credit for tax paid to foreign countries, so Indian or Canadian tax is relieved only on the federal return.

Spouses in different states. If you file a joint federal return and one spouse is a full-year Illinois resident and the other is not, you can file separate Illinois returns, dividing income and deductions. A joint Illinois return treats both as residents, and the choice is irrevocable for the year.

Nexus for businesses

Illinois defines physical presence broadly: an office, distribution house, sales house, warehouse or other place of business, or an agent or representative operating in the state, even temporarily. A remote retailer is an out-of-state seller with $100,000 or more of gross receipts from Illinois buyers; the 200-transaction test was removed effective January 1, 2026. On the income tax side, a federal law known as P.L. 86-272 can protect a seller of tangible goods whose only state activity is soliciting orders; the IL-1120 has a box for sales into Illinois that are protected. Services and software are treated differently, so analyse each.

A corporation qualified to do business in Illinois, and required to file a federal return, must file Form IL-1120 whether or not it has net income. A foreign corporation follows the same filing rules as a domestic one. See foreign qualification in Illinois.

How to review multistate exposure, step by step

1. Map people and places by month: where each owner and employee lived, worked and traveled.
2. Decide domicile or residency for each person in each state.
3. Source each income item: wages by work location, business income by apportionment, rents by property location, interest by residence.
4. Check reciprocity and credits: Iowa, Kentucky, Michigan and Wisconsin are exempt for wages; use Schedule CR for other states.
5. Register for payroll in each state where employees work: income tax withholding and unemployment insurance. See the Illinois payroll guide.
6. Test sales tax thresholds in each state where you sell, plus inventory and employee locations. See Illinois sales and use tax.
7. File returns and make estimates on time in each state.
8. Document moves, travel logs and customer locations.

Documents you need

• Employer W-2s showing state wages and withholding
• Moving dates, lease or deed, driver's license and voter registration history
• Work-location logs, including remote work days
• Sales by ship-to state, inventory locations and employee addresses

Deadlines and penalties

Illinois individual returns follow the federal calendar: April 15, with an automatic six-month extension to file that does not extend time to pay. Other states set their own dates, rates and penalties; check each tax agency. Failing to register or file where nexus exists can lead to back tax, penalties and interest. See the Illinois compliance calendar.

India, Canada and the states

See also hiring US employees from abroad.

Worked examples

Priya, Aurora resident, works at her employer's Kenosha, Wisconsin office. Wisconsin is a reciprocal state. She asks the employer to stop Wisconsin withholding, files only an Illinois return, and includes the wages in Illinois income. If Wisconsin tax was withheld anyway, she claims a refund from Wisconsin; it is not a credit on Schedule CR.

Rohit, Naperville, works two weeks a month at a client site in Indiana. Illinois taxes him as a resident. If Indiana taxes the Indiana-source wages and he files an Indiana return, he claims Schedule CR on his IL-1040 for the Indiana tax, limited as the instructions explain.

A Mumbai software firm with two engineers in Naperville. The employees create physical presence: it registers for Illinois withholding and UI, withholds from wages and, if a corporation, may need to qualify to do business and file Form IL-1120. If it also sells taxable goods to Illinois customers it evaluates sales tax.

Mistakes to avoid

• Claiming Schedule CR for Indian or Canadian tax.
• Treating a reciprocal state's withholding as an Illinois credit.
• Assuming remote employees create no nexus.
• Ignoring the move date in a part-year year.
• Treating P.L. 86-272 as a shield for services or software.

How we can help

Our Aurora, Illinois firm sorts out residency and nexus for individuals and businesses, prepares IL-1040 with Schedules NR and CR, advises on state registrations and handles IDOR correspondence. We coordinate with your Indian CA or Canadian CPA so foreign and state returns agree. See our state tax representation service and the Aurora local guide.

Frequently asked questions

General information only. It is not tax, legal, accounting or immigration advice for your situation, and rules change; confirm the current rules with the official source or a licensed professional in the relevant country.