Illinois imposes a flat 4.95% individual income tax rate on all net income - there are no graduated brackets. Illinois is one of the most taxpayer-friendly states for retirees because it completely exempts retirement income: Social Security benefits, pension income from government and private plans, and distributions from 401(k), IRA, and other qualified retirement accounts are all excluded from Illinois taxable income. A retiree with $200,000 of pension and retirement plan income pays zero Illinois income tax on that amount. But Illinois has significant quirks - it does not allow most federal itemized deductions, it conforms differently to federal tax law, and Chicago imposes its own city-level taxes.
Rate: 4.95% flat rate on all net income. No graduated brackets. No lower rate for capital gains (unlike federal law where long-term gains are taxed at 0/15/20%). All income taxed at the same 4.95%.
Personal exemption: $2,425 per taxpayer (and per dependent). Not the same as the federal standard deduction - Illinois has its own exemption system and does not use the federal standard or itemized deductions framework.
Retirement income exemption: Social Security, pensions from any employer (public or private), 401(k) distributions, IRA distributions, railroad retirement benefits, and military retirement pay are all completely exempt from Illinois income tax. No income threshold. No age requirement.
Illinois uses a "starting point" approach: Illinois net income starts with federal adjusted gross income (line 11 of Form 1040) and then applies Illinois-specific additions and subtractions. Illinois does not allow the federal standard deduction or itemized deductions. Instead, Illinois allows only: the personal exemption ($2,425 per person), a property tax credit (5% of Illinois property tax paid), an education expense credit (limited), and the specific retirement income subtractions.
Illinois does not conform to the federal NOL rules - Illinois has its own NOL carryforward rules that differ from the federal indefinite carryforward. Illinois also does not allow the federal §199A QBI deduction. Illinois capital gains are taxed at 4.95% regardless of holding period - there is no Illinois preferential rate for long-term gains.
Illinois has its own separate estate tax with a $4 million exemption - dramatically lower than the federal $15 million exemption under OBBBA. Illinois estate tax rates are graduated from 0.8% to 16% on amounts above the exemption. An Illinois resident with a $10 million estate owes zero federal estate tax (under the $15 million federal exemption) but owes Illinois estate tax on $6 million at rates up to 16%. Illinois estate planning must account for this separate state-level tax obligation that federal planning alone does not address.
Chicago and Cook County impose additional taxes on top of Illinois state taxes. The Chicago personal property lease transaction tax applies to cloud computing services and SaaS. Chicago's amusement tax applies to streaming services (Netflix, Spotify, etc.) at 9%. The City of Chicago also has its own business tax obligations for businesses operating within city limits. These municipal taxes are separate from and in addition to Illinois state income tax.