Before you start

An SSN or ITIN
Form W-4 with your employer for federal withholding
Illinois Form IL-W-4 for state withholding
Records of foreign income and foreign financial accounts

Step-by-step

1
Complete the W-4 and IL-W-4 on day one
These set your federal and Illinois withholding. Illinois's flat rate makes state withholding simple, but the federal form still needs care in a two-income household.
Via employerWho: YouFirst week of employment
2
Determine your US tax residency
The substantial presence test counts weighted days over three years to decide whether the US taxes your worldwide income or only US-source income. Your visa does not decide this.
OnlineWho: You
3
Check for an applicable tax treaty
The US has treaties with around 70 countries that can reduce or exempt tax on particular income types. Treaty benefits are claimed on your return, not granted automatically.
OnlineWho: You
4
File federal and Illinois returns by 15 April
The tax year is the calendar year. Illinois's flat rate makes the state return one of the simplest in the country. An extension moves the filing date, not the payment date.
OnlineWho: YouBy 15 April annually
5
File an FBAR if foreign accounts exceed $10,000
Aggregate foreign account balances over $10,000 at any point in the year trigger a FinCEN filing, separate from your tax return.
OnlineWho: You
6
Look up the real property tax before you buy
The Cook County Assessor publishes each property's assessment and tax history. Use it rather than a listing's estimate — reassessment cycles can move a bill sharply, and appeals are a routine part of owning here.
OnlineWho: You

Documents you’ll need

Form W-2 from each employer, issued by 31 January
Form 1099s for freelance, interest and investment income
Passport and travel history for the substantial presence day count
Foreign account statements for FBAR reporting
Cook County property tax bills, if you own

Things most newcomers don’t know

The flat rate is constitutional, not just legislative.

The Illinois constitution requires a non-graduated income tax. A 2020 ballot measure to permit graduated rates was defeated, so changing it needs a constitutional amendment rather than an act of the legislature. For a high earner planning long term, that durability matters as much as the rate.

Source: Illinois Department of Revenue

Chicago has no city income tax, unlike New York or Philadelphia.

Both of those stack a municipal income tax on top of state and federal — NYC up to 3.876%, Philadelphia around 3.74% for residents. Chicago does not. Comparing big-city US salaries on state rate alone misses this, and it works in Chicago's favour.

Source: Illinois Department of Revenue

Property tax is where Illinois actually collects.

Effective property tax rates in Cook County are among the highest in the United States, and the three-year reassessment cycle can move a bill materially in one year. It reaches renters through the rent. A low flat income tax alongside high property tax is a genuine trade, not a free lunch.

Source: Cook County Assessor

Your visa does not determine your tax residency.

The substantial presence test — a weighted day count across three years — decides whether the US taxes your worldwide income. Someone on a temporary visa can be a US tax resident; someone on a long visa can fail the test.

Source: IRS — substantial presence test

Common mistakes to avoid

Comparing Chicago against a no-income-tax city without accounting for property and sales tax on both sides.
Buying property on a listing's estimated tax figure rather than the assessor's record.
Assuming your visa type settles your tax residency.
Missing the FBAR because a home-country account did not feel 'foreign'.
Believing a filing extension also extends the payment deadline.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.