Chicago property tax appeal deadlines are set township by township, not by one citywide date. When the Cook County Assessor’s Office opens your township for appeals, you typically have 30 days to file.1Cook County Assessor’s Office. Overview of How Appeals Work Miss that window and a separate appeal period later opens at the Cook County Board of Review. If that one doesn’t go your way either, a third option exists at the state level through the Illinois Property Tax Appeal Board. The job is figuring out which window applies to you and watching the Assessor’s calendar, because the exact dates shift every year.
How the Township Calendar Works
Chicago is divided into several townships, including Rogers Park and Lake among others, and each one opens and closes for appeals on its own schedule. The Assessor’s Assessment and Appeal Calendar tracks every township’s status in real time and lists the last day to file for each.2Cook County Assessor’s Office. Assessment and Appeal Calendar
When your township opens, you’ll receive a reassessment notice in the mail. It carries the Assessor’s updated estimate of your home’s market value, the property characteristics on file, and the specific date your appeal is due. From the day the township opens, you generally have 30 days.1Cook County Assessor’s Office. Overview of How Appeals Work Those dates move year to year depending on how quickly the Assessor’s Office processes each area, so checking the calendar regularly is the only reliable way to catch them.
One practical warning: don’t start an online appeal file before your township officially opens. Files started early can be deleted.3Cook County Assessor’s Office. File an Appeal Online Wait for the calendar to show your township as open, then file within the posted window.
What 2026 Looks Like for Chicago Homeowners
Cook County reassesses on a three-year rotating cycle. The county is divided into three triads: the north and west suburbs, the south and west suburbs, and the City of Chicago. Each triad is reassessed once every three years, so roughly one-third of properties get new valuations annually.4Cook County Assessor’s Office. About the Cook County Assessor’s Office In 2026, the south and west suburbs are the triad being reassessed. Chicago properties are not scheduled for reassessment in 2026 unless a specific change triggers one, such as a building permit or a property subdivision.2Cook County Assessor’s Office. Assessment and Appeal Calendar
That doesn’t leave Chicago homeowners with nothing to do. The Board of Review runs its own appeal schedule and accepts filings for Chicago townships even in a non-reassessment year. And if your property was reassessed in 2024, Chicago’s most recent reassessment year, a Board of Review window tied to that assessment may still be in play depending on where the calendar sits.
If You Missed the Assessor’s Deadline: The Board of Review
The Cook County Board of Review is a separate agency from the Assessor, and it opens its own appeal window regardless of what happened at the first level. Homeowners who missed the Assessor’s deadline, or who filed and got an unfavorable result, can appeal here instead. The Board also accepts appeals from homeowners who skipped the Assessor-level filing entirely.2Cook County Assessor’s Office. Assessment and Appeal Calendar
The Board of Review’s window for a given township typically opens several months after the Assessor’s window closes. Filing dates for both appear on the same Assessment and Appeal Calendar, so one page covers both deadlines. The Board accepts evidence on the same grounds the Assessor does: overvaluation, lack of uniformity, recent purchase, factual errors, and special circumstances.5Cook County Board of Review. How to Present a Case It’s a genuinely independent review rather than a rubber stamp of the Assessor’s decision.
If the Board of Review Rules Against You: PTAB
One more administrative step remains before any courtroom. The Illinois Property Tax Appeal Board (PTAB) accepts appeals from property owners dissatisfied with any Board of Review decision. You have 30 days from the postmark date of the Board of Review’s written decision to file your PTAB petition.6Illinois Property Tax Appeal Board. Frequently Asked Questions
PTAB proceedings are de novo, meaning the board considers your case from scratch as if the Board of Review never heard it. You’re not stuck arguing the Board of Review made a mistake; you can present all your evidence fresh. There’s a catch, though. All written and documentary evidence you intend to rely on must be submitted with your petition, or you need to request an extension in writing at the time of filing. For Cook County appeals, PTAB also requires two copies of the Board of Review’s final decision along with the petition.7Illinois Property Tax Appeal Board. Practice and Procedures
So the 30-day PTAB clock starts from the postmark on the Board of Review’s decision letter, not the day you open the envelope. If you plan to go this route, start assembling your evidence before the decision arrives.
After All Deadlines Have Passed: Certificates of Error
Missing every appeal window isn’t always the end. If you later discover a factual error in a past year’s assessment, the Cook County Assessor can issue a Certificate of Error to correct the assessed value for that specific prior year. Each certificate covers only one tax year, so an error that affected multiple years means a separate application for each.8Cook County Assessor’s Office. What Is a Certificate of Error and How Can I Apply for One
The process takes longer than a standard appeal. If the Board of Review previously reviewed that year’s assessment, the Board also has to approve the certificate. Non-residential corrections that would reduce assessed value by more than $100,000 go to the Circuit Court for a judge’s review.8Cook County Assessor’s Office. What Is a Certificate of Error and How Can I Apply for One Application forms are available on the Assessor’s website or by calling (312) 443-7550.
A Certificate of Error is for fixing specific factual mistakes, like wrong square footage or an extra bathroom that doesn’t exist, not for re-litigating a valuation you simply disagree with. If the number was wrong because the Assessor had the wrong facts, this is the path. If the number was wrong because you think the market value was too high, the regular appeal windows are where that argument belongs.
Keeping Track
Three deadlines, three agencies, one calendar page for the first two. Check the Assessor’s Assessment and Appeal Calendar at least once a month if you’re planning to appeal, because the township windows open on their own schedule and the 30-day clock is short. Watch your mail during your township’s expected opening for the reassessment notice; it will carry the exact date. And if a Board of Review decision arrives in your mailbox, note the postmark immediately, because that’s the day your 30-day PTAB window started running.