How to Appeal Your Property Taxes in Cook County (2026 Guide)

Cook County is the only major property tax jurisdiction in the country where the correct answer to "when is the deadline" is a question back at you: which township are you in?

That is not an administrative quirk. It is written into the statute, and understanding it is the difference between filing and being locked out.

There is no Cook County deadline

Texas gives every county a single May 15 protest deadline. Illinois gives you nothing of the kind.

Under 35 ILCS 200/16-115, complaints in Cook County are filed by township, on the dates set out in the notices issued under §16-110. The Assessor publishes each township's window on a rolling calendar through the year, and geographically adjacent townships can open months apart. Your neighbor's timeline is not your timeline if you are in different townships.

Outside Cook, the rule is different again: 35 ILCS 200/16-55 sets the deadline at on or before 30 calendar days after publication of the assessment list for the township. Still no statewide date.

The only reliable move is to check the Assessor's published calendar at cookcountyassessoril.gov/assessment-calendar-and-deadlines for your township's dates, and to confirm which reassessment region you are in rather than assuming.

It is a complaint, not an appeal

Small point, real signal. The statutory term at the Assessor and Board of Review level is complaint, not appeal (§16-55, §16-95, §16-115). "Appeal" is the correct word only once you reach the Property Tax Appeal Board or Circuit Court. Cook's Assessor website says "appeal" colloquially, so both words are in circulation, but the filings are complaints.

The two stages, and why the second one matters

Stage one: the Assessor. When your township's window opens, you file a complaint with the Cook County Assessor with your Property Index Number (PIN) and evidence that the valuation is too high. This stage is optional. You are not required to go through the Assessor before the Board of Review.

Stage two: the Board of Review. The Board of Review opens its own window for each township, and it is a separate body from the Assessor. Its authority to review and correct on written complaint sits in 35 ILCS 200/16-95. It decides on the evidence filed with it. An Assessor denial is not a finding the Board of Review is reviewing for error.

You can file at both stages, or skip the Assessor and file only with the Board of Review, which matters if the Assessor's window for your township has already closed.

After the Board of Review: PTAB. Under 35 ILCS 200/16-160, you file with the Property Tax Appeal Board within 30 days of the Board of Review's written decision. This applies in every Illinois county. PTAB is a formal administrative proceeding. There is also an alternative Circuit Court route under 35 ILCS 200/23-5 and 23-10, a pay-under-protest tax objection, available after you exhaust the Board of Review.

The 10% number, and why Cook is different

Illinois' statutory level of assessment is 33⅓% of fair cash value under 35 ILCS 200/9-145, for every county except classifying counties. Cook is the classifying county. Under the Cook County Classification Ordinance, Cook County Code ch. 74 §74-63, residential property (Class 2) is assessed at 10% of fair market value.

So the arithmetic on your notice: an assessed value of $25,000 means the Assessor has concluded your home's fair market value is $250,000. Argue the $250,000. That is the number your comparable sales speak to.

Because Cook assesses at 10% while the rest of Illinois assesses at 33⅓%, the Illinois Department of Revenue applies an equalization factor, commonly called the multiplier, to bring Cook's equalized assessed values onto a comparable footing with other counties for purposes that cross county lines. You cannot appeal the multiplier. It is set by the state. What you can do is reduce the assessed value it gets applied to.

The constitutional backstop is Ill. Const. art. IX, §4, which requires uniformity in real property valuation and requires that classification in counties over 200,000 be reasonable and uniform.

The evidence standard, which is case law

Illinois' burden of proof is not in the Property Tax Code. It comes from Kankakee County Board of Review v. Property Tax Appeal Board, 131 Ill. 2d 1 (1989), and it splits by theory:

• Overvaluation: preponderance of the evidence.
• Lack of uniformity: clear and convincing evidence.

That split should shape your filing. The uniformity argument, that your property is assessed at a higher percentage of market value than comparable properties nearby, carries a materially heavier burden than the straightforward overvaluation argument. Lead with overvaluation and comparable sales. Add uniformity as a supporting theory, not as your only one, unless the disparity is stark and well documented.

Neither standard appears in the Property Tax Code itself, so if you need to point to authority, cite Kankakee rather than a 35 ILCS section number.

What to file

• Comparable sales. Three to five arm's length sales, similar size, age, construction type, lot, and bed/bath count, within roughly half a mile and the last 12 to 18 months. Sale prices, not listings.
• Record errors. Wrong square footage, wrong classification, wrong physical description. The cleanest correction available.
• Condition. Structural problems, deferred maintenance, flood damage. Photos, repair estimates, contractor quotes.
• Specificity. File online, keep copies of your full submission, and be prepared to reproduce it at PTAB.

Check your PIN before your window opens

We hold live parcel and assessment data for all 1,586,697 Cook County parcels. Run your address through the free calculator and it pulls comparable properties from public records and shows you where your assessed value sits against them, in market-value terms. Free, about 30 seconds, no signup.

If you are over-assessed, file the complaint yourself for free, or use the $49 flat kit for a filing-ready evidence packet you can submit at the Assessor stage, the Board of Review stage, or both. If you are fairly assessed, you learned that for free.

The one thing that cannot be fixed after the fact is a missed window. Find your township's dates on the Assessor's calendar first. For the statewide process and Board of Review detail, see our Illinois property tax appeal guide.

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