Cook County Property Tax Appeal Deadlines: Windows and Filing

In Cook County, the property tax appeal deadline is generally 30 days from the date your reassessment notice is mailed, and that date is printed on the notice itself.¹ There is no single countywide date. Each of the county’s 38 townships opens and closes its own window, so your deadline depends entirely on where your property sits.²

How Your Township’s Deadline Gets Set

Cook County reassesses property on a three-year rotation. The City of Chicago, the north and northwest suburbs, and the south and west suburbs each take a turn. In 2026, the south and west suburban townships are being reassessed.²

When the Assessor finishes a township, reassessment notices go out to every owner in it. Your notice lists the new assessed value and the last day you can appeal. The window is generally 30 days, but the actual dates shift from township to township based on when the Assessor completes the review.¹

You do not have to wait for a reassessment year to appeal. Even in the two off-years, the Assessor opens an appeal window for your township on a published schedule. The Assessment and Appeal Calendar on the Assessor’s website posts opening and closing dates as they become available.² Check it early. Once your township closes, it does not reopen until the next cycle.

Two Deadlines, Not One: Assessor and Board of Review

This is where most people get caught. Cook County gives you two separate chances to appeal the same tax year, each run by a different office and each with its own filing window.²

The Assessor’s Window Opens First

Once reassessment notices for your township go out, you have roughly 30 days to file with the Cook County Assessor’s Office. Filing is free and can be done online.¹ A reduction here becomes your new assessed value going forward. If the Assessor denies you or offers a smaller reduction than you wanted, you still get a second shot at the Board of Review.

The Board of Review Window Opens After

After the Assessor finishes a township, the Board of Review opens its own window for that same township. Under Illinois law, a complaint to the Board of Review must be filed within 30 calendar days after the assessment list is published.³ The Board posts its own schedule of township deadlines, and it conducts an independent review, so a denial at the Assessor level does not bind it.

You can file at both levels for the same year, and many homeowners do. Skipping the Assessor’s appeal does not disqualify you from the Board of Review, and filing with the Assessor first does not weaken your Board case.

How to File, and How to Prove You Were on Time

The Assessor’s online portal takes about 20 minutes: enter your Property Index Number, pick a reason for the appeal, upload your evidence, and sign digitally. You get a confirmation when the filing goes through.¹

The Board of Review has its own system, the Digital Appeals Processing System (DAPS). You create a separate account, enter your property information, attach evidence, and submit.⁴ The two systems are not connected. Filing with one does not file with the other.

Paper filings are still accepted at either office. If you mail, use certified mail so you have a postmark receipt. Late submissions are rejected regardless of the reason, and an unverified “I mailed it on time” will not save a missed deadline.

After you file, decisions typically take several weeks to a few months, depending on how many appeals come in for your township. Results arrive by mail or email.

What to Have Ready Before the Window Opens

You will need your 14-digit Property Index Number (PIN) to file anything. It appears on your tax bill, your deed, and any notice from the Assessor.⁵ If you cannot find it, look it up by address on the Cook County Treasurer’s website.⁶

Appeals generally rest on one of three arguments:

Overvaluation. The Assessor’s market value estimate is too high. A recent appraisal, a closing statement from a recent purchase, or lower comparable sales in your area all support this.
Lack of uniformity. Similar properties nearby are assessed at a lower level than yours. You will need comparables with lower assessed values despite similar size, age, condition, and location.
Factual errors. The Assessor has the wrong square footage, lot size, bedroom count, or building classification. Correcting these can lower the assessment without any sales comparison. Pull up your PIN on the Assessor’s website to see what they have on file.

Gather the evidence before your window opens. Scrambling in the last 48 hours is how deadlines get missed.

If You Lose or Miss the Board of Review Deadline

If the Board of Review denies your appeal or grants less than you wanted, you have 30 days from receiving the written decision to file a petition with the Illinois Property Tax Appeal Board (PTAB).⁷ PTAB is a state-level body that reviews independently. It can raise as well as lower an assessment, so it is not a risk-free step.

The alternative is a tax objection lawsuit in the Circuit Court of Cook County, heard in the County Division under rules specific to tax objection proceedings.⁸ Court litigation costs more and takes longer than the administrative route, and it is generally used for high-value commercial properties or cases turning on legal questions PTAB is not suited to resolve.

The 30-day PTAB clock runs from the postmark on the Board of Review’s decision letter. Open that letter the day it arrives and put the deadline on your calendar. If you miss it, the Board of Review’s decision stands for that tax year.

When a Successful Appeal Shows Up on Your Bill

Cook County bills property taxes in arrears, so filing on time this year affects a bill you receive next year. A reduction does not come back as a refund check. It appears as a lower second-installment bill the following year.⁹

The first installment, due in early March, is fixed by law at 55 percent of the previous year’s total tax and reflects no appeal results. The second installment, due in late summer, is where new assessments, rates, exemptions, and appeal reductions get reconciled.⁹ So an appeal of your 2025 assessment, filed in your 2025 township window, lowers your 2026 second-installment bill.

If a bill goes out before an appeal is resolved, a Certificate of Error can adjust it after the fact, producing either a credit or a refund.¹⁰Cook County Assessor’s Office. Certificates of Error

1
Cook County Assessor’s Office. Overview of How Appeals Work
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Cook County Assessor’s Office. Assessment and Appeal Calendar
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Illinois General Assembly. 35 ILCS 200 Property Tax Code – Section 16-55
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Cook County. Board of Review Launches Assessment Appeals with State of the Art Digital Appeals Processing System
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Cook County Assessor’s Office. Where Do I Find My PIN
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Cook County Treasurer’s Office. About Your Property Index Number (PIN)
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Property Tax Appeal Board. PTAB Practice and Procedures
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Circuit Court of Cook County. Real Estate Tax Proceedings
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Cook County Assessor’s Office. Your Assessment Notice and Tax Bill
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