Illinois Tax Obligations Most Chicago-Area Small Business Owners Are Missing

Filing your federal taxes and calling it done is one of the most common (and costly)  mistakes small business owners  make.

Illinois has its own separate set of tax obligations. Most owners are meeting some of them, missing others, and not totally sure which is which. Here’s the plain-breakdown.

Illinois Income Tax

Illinois taxes business income at a flat rate:

• Sole proprietors, single-member LLCs, S-corps: 4.95%
• C-corporations: 9.5% (7% corporate income tax + 2.5% personal property replacement tax)
• S-corps also owe a 1.5% personal property replacement tax on net income — separate from what individual owners pay

These are on top of federal taxes. If you’re calculating your total tax burden, don’t forget to layer Illinois in.

Illinois Quarterly Estimated Payments

Just like the IRS, Illinois requires quarterly estimated payments if you expect to owe tax. These go to the IDOR portal at mytax.illinois.gov,  completely separate from federal payments. Deadlines mirror the IRS schedule. A lot of owners pay the IRS quarterly and skip IDOR entirely. That’s a penalty waiting to happen.

Chicago vs. Suburban Business Obligations

If you operate within Chicago city limits, you need a City of Chicago business license – renewed annually, and fines apply if you’re operating without one. Outside the city, Oak Brook, Naperville, Schaumburg, and other suburbs have their own municipal licensing requirements. Check with your village or city clerk.

Illinois Sales Tax

The state base rate is 6.25%, but Cook County adds to that, and Chicago city adds more on top. If you’re selling taxable goods or certain services, you’re responsible for collecting and remitting the correct rate based on where the transaction occurs — not where your business is located.

Payroll Tax Obligations

If you have employees, you’re also responsible for:

• Illinois income tax withholding
• Registration with IDES (Illinois Department of Employment Security) for unemployment insurance
• Reporting new hires to the Illinois New Hire Reporting Center
• Chicago minimum wage compliance ($16.20/hr as of July 1, 2026) vs. statewide minimum ($15.00/hr)

At JIL & Associates, we specialize in tax compliance and bookkeeping for small businesses across the Chicago area. We’ll help you make sure you’re meeting every Illinois obligation — and not paying more than you owe. 📞 Call (630) 828-3648 or visit jiladvisors.com to schedule a compliance review.