Illinois & Cook County Property Tax Appeal: The Complete Guide

Cook County, Illinois — home to Chicago and roughly 1.8 million parcels — has one of the highest effective property tax burdens and one of the most active appeal cultures in the United States. It is also unusually complicated: assessments run on a three-year cycle, there are two separate appeal bodies before you ever reach a court, and every deadline is set township by township. This guide explains how it actually works.

The triennial reassessment cycle

The Cook County Assessor reassesses property once every three years, on a rotating regional schedule. Knowing where you sit in the cycle tells you when your value is most likely to jump:

In a reassessment year, the Assessor mails a Reassessment Notice with a new fair market value. That notice is your cue to consider an appeal — but you do not have to wait for a reassessment year to appeal (more on that below).

The two-level appeal (before any court)

Cook County has two separate administrative appeal bodies, and they are independent of each other:

1. Cook County Assessor's Office — In a reassessment year, when your township's appeal window opens you can file an appeal directly with the Assessor for roughly 30 days after your Reassessment Notice is mailed. This is the fastest, lowest-friction level.
2. Cook County Board of Review — A separate elected body that hears appeals after the Assessor's window closes, on its own township-by-township schedule (also about 30 days per township). Crucially, the Board of Review opens every year, so this is where you appeal in non-reassessment years.

You can appeal at the Board of Review whether or not you appealed at the Assessor's Office — and many owners who don't get the reduction they want from the Assessor simply re-file at the Board of Review for a second review.

Township-by-township deadlines

There is no single county-wide deadline. Each township opens and closes on its own dates, published on the Assessor's Assessment & Appeal Calendar and the Board of Review's calendar. Windows typically run about 30 days from the date notices are mailed for that township. For example, in the 2026 south/west suburban reassessment, townships such as Cicero, Stickney, and Lyons each had their own closing dates spread across the summer. Always confirm your township's exact window before you rely on any date.

What wins a Cook County appeal

Cook County appeals succeed on two grounds, and you can argue either or both:

• Lack of uniformity — your home is assessed higher than comparable nearby homes. This is the workhorse argument in Cook County: you show 3–6 similar properties (same neighborhood, size, age, style) with lower assessed values per square foot.
• Overvaluation (market value) — recent sales of comparable homes, or a recent purchase price, show your fair market value is lower than the Assessor's estimate.

Beyond the Board of Review: PTAB and Circuit Court

If the Board of Review's decision still doesn't satisfy you, Illinois gives you two further options:

• Illinois Property Tax Appeal Board (PTAB) — a state-level board. You generally must file within 30 days of the Board of Review's final decision. PTAB review is free to file and is the most common next step.
• Circuit Court — you may instead file a tax objection in court, but you must pay the tax under protest first. This route is usually reserved for larger or commercial cases and typically involves an attorney.

Don't forget exemptions — they're separate from appeals

Appealing your assessed value is different from claiming an exemption. Cook County homeowners should make sure they also have every exemption they qualify for — the Homeowner Exemption, the Senior Exemption, and the Senior Freeze (Low-Income Senior Citizens Assessment Freeze) — because these reduce your taxable value on top of any appeal. Illinois raised the general homestead exemption to $8,000 of equalized assessed value in Cook and the collar counties. Check the Property Tax Edge Exemptions Database for the current amounts and filing steps.