Illinois uses a flat state income tax of 5.0% in 2026 — the same rate applies to every dollar of taxable income, which makes your paycheck easy to predict. On a $75,000 salary, a single filer pays about $3,713 in state tax and takes home roughly $57,880 a year (about 77.2% of gross) after federal, state, and FICA withholding.

Illinois's 5.0% rate is above the 4.8% average among states that tax wage income. Because the rate is flat, a raise never pushes part of your income into a higher state bracket — every extra dollar is taxed at the same 5.0%, unlike the federal system where higher earnings hit progressively higher brackets.

Remember that FICA is separate from income tax and is not affected by your state. Every worker pays 6.2% for Social Security on the first $184,500 of wages (the 2026 wage base) plus 1.45% for Medicare on all wages. Pre-tax 401(k) and HSA contributions lower your federal and state income tax but do not reduce FICA — a detail that trips up a lot of first-time budgeters.

Illinois' flat income tax isn't just policy — it's constitutional. The state constitution requires a single rate for all filers, and a 2020 ballot measure to allow graduated rates was rejected by voters. That makes Illinois' rate unusually stable and predictable. The counterweight is property tax: Illinois consistently ranks at or near the highest effective property tax rates in the nation, so homeowners feel the state's tax burden through their escrow payment far more than their paycheck.