Missed Your Cook County Property Tax Appeal Deadline? Here's What You Can Still Do
The envelope arrived. You opened it, saw your reassessment notice, and set it aside meaning to deal with it later. Now you're looking at the calendar and realize with a sinking feeling: you missed the deadline.
If you missed your Cook County property tax appeal deadline, you're not alone—and you still have options. Here's exactly what you can do, what you can't do, and how to make sure this never happens again.
Understanding What You Missed
The 30-Day Deadline
Cook County property owners typically have 30 days from receiving their reassessment notice to file an appeal with the Assessor's Office. This deadline is printed directly on your notice.
But here's what many homeowners don't realize: if you miss your appeal period in your reassessment year, you may appeal the following year when your township is open for appeals.
Cook County's Two-Stage Appeal Process
Cook County has a two-stage appeal process, and missing the first deadline doesn't necessarily lock you out completely:
Stage 1: Cook County Assessor's Office
This is the 30-day window from your notice
Stage 2: Cook County Board of Review
This opens later, typically in summer/fall, and gives you another opportunity
Option 1: Appeal to the Board of Review (If Still Open)
The Good News
Even if you missed the Assessor's deadline, you can file directly with the Cook County Board of Review when your township opens for appeals.
The Board of Review is a separate, quasi-judicial agency independent of the Assessor, and you are at no disadvantage if the Assessor has granted or denied a request to reduce the assessment. This means you can skip the Assessor entirely and go straight to the Board.
When Does the Board of Review Open?
The Board of Review operates on a township-by-township schedule, typically opening from late summer through early winter. The pre-file period for non-attorneys begins in late June, and allows all filers to submit their appeal before each township officially opens.
How to check if your township is still open:
- Visit the Cook County Board of Review website
- Look up your township's filing window
- Note the closing date—you must file before this date
Important: You can pre-register for notifications to be alerted by the Board of Review of the opening and closing filing periods for your respective township.
Option 2: File a Certificate of Error (For Specific Situations)
If You've Missed Both Deadlines
If you've missed both the Assessor's deadline AND the Board of Review deadline, you still have one option for certain types of errors: a Certificate of Error (CoE).
What is a Certificate of Error?
A Certificate of Error allows the Cook County Assessor to change a property's assessed value for a prior year as a way to correct a tax bill after the assessment for that tax year is finalized.
When Can You Use a Certificate of Error?
Certificates of Error are available for:
- ✓Mathematical errors in your assessment
- ✓Incorrect property descriptions (wrong square footage, number of rooms, etc.)
- ✓Duplicate assessments
- ✓Property damage or destruction that wasn't reflected
- ✓Missing exemptions you were eligible for but didn't receive
When CAN'T You Use a Certificate of Error?
There are some instances that cannot be remedied by a Certificate of Error, including "errors of judgment as to the valuation of the property." This means you generally cannot use a CoE for:
- ✗Disputing your property's market value
- ✗Arguing lack of uniformity compared to neighbors
- ✗General overassessment without a clear factual error
How to File a Certificate of Error
You can file online if you are submitting a Certificate of Error with an appeal filing for the current year, and the option to include a Certificate of Error filing is within the appeal application. Otherwise, you can file separately through the Assessor's office.
Processing time: If the property's assessment has been previously reviewed by the Board of Review, the Board of Review must approve the Certificate of Error as well, and non-residential Certificate of Error requests that seek a reduction of more than $100,000 in assessed value must be sent to the Circuit Court for a judge's consideration.
Contact: Assessor's Taxpayer Resolution Department at Assessor.Taxpayer.Resolution@cookcountyil.gov
Option 3: Wait Until Next Year's Appeal Window
This Is the Option No One Wants to Hear
Sometimes it's your only choice. Here's how it works:
Cook County follows a triennial reassessment cycle, but Illinois law allows property owners to appeal annually, even in years when their township isn't reassessed.
This means if you miss the deadline in 2025, you can appeal in 2026. You don't need to wait for your next triennial reassessment—your township will have appeal windows each year.
The Cost of Waiting
If your property is overassessed and you wait a year to appeal, you'll pay the higher property taxes for that year. For example:
- Overassessed by $10,000 in assessed value
- Effective tax rate of ~2% in your area
- You'll overpay approximately $2,000 for that year
That money is gone forever—you won't get it back even if you successfully appeal the following year.
What You CANNOT Do
Let's be clear about what won't work if you've missed your deadlines:
You Cannot Appeal Directly to PTAB
To file an appeal with the Illinois Property Tax Appeal Board (PTAB), you must have first filed an appeal with the Cook County Board of Review and received a final decision. PTAB only reviews decisions made by the Board of Review and cannot accept new cases directly from property owners who missed the Board of Review filing window.
You Cannot File Late and Hope for Leniency
The Board's jurisdiction is limited by law to the current year. Cook County is strict about deadlines. If you miss the filing window, your appeal will be rejected—there are no exceptions for "I was busy" or "I didn't know."
You Cannot Get a Refund for Prior Years
Even if you successfully appeal next year, you won't receive a refund for the overpaid taxes from this year. Your reduction will only apply going forward.
Real-World Example: What Happens When You Miss the Deadline
Mike's Story
Mike owns a bungalow in Jefferson Park.
His 2025 reassessment showed his assessed value jumped from $32,000 to $42,000—a 31% increase. His notice arrived in February with a March 15 deadline.
The Problem:
Mike planned to appeal but got busy at work. By the time he remembered in April, the Assessor's deadline had passed.
What Mike Did:
- He checked the Board of Review calendar and found his township would open in September
- He gathered his evidence: comparable sales showing his home was overassessed by $8,000
- He filed with the Board of Review in September
- He received a reduction to $36,000 in November
The Cost of Missing the First Deadline:
Mike still saved money, but he paid higher taxes on the second installment (due in July/August) before his reduction was applied. This cost him approximately $400 that he could have saved if he'd appealed at the Assessor level.
The lesson: Missing the Assessor deadline cost him money but didn't prevent him from getting relief.
How to Make Sure This Never Happens Again
Set Multiple Reminders
When you receive your assessment notice:
- Immediately enter the deadline in your phone calendar
- Set reminders for 7 days before, 3 days before, and the day before
- Treat this deadline like a tax return deadline—it's that important
Never Miss Another Deadline
Don't let this happen again. Our property monitoring service alerts you the moment your assessment is published and tracks all appeal deadlines automatically—so you get the full 30 days to prepare instead of scrambling at the last minute.
Think about Mike's situation: he lost $400 by missing his deadline. Our monitoring costs less than that per year and ensures you never miss an opportunity to save.
Learn More About Monitoring →Your Action Plan If You Missed the Deadline
Here's what to do right now:
Step 1: Determine Which Deadline You Missed
- Missed the Assessor deadline (30 days from notice)? → Check if Board of Review is open
- Missed both Assessor and Board of Review? → Check if you qualify for Certificate of Error
- Both are closed and no CoE applies? → Plan to appeal next year
Step 2: Check the Board of Review Status
Visit cookcountyboardofreview.com/dates-and-deadlines and:
- Find your township
- Look for opening and closing dates
- If still open, file immediately
- If closed, note next year's expected timeline
Step 3: Evaluate Certificate of Error Eligibility
If you have:
- Incorrect property data (wrong square footage, rooms, etc.)
- A missed exemption (Homeowner, Senior, Disability, etc.)
- Clear mathematical errors
- Property damage not reflected in assessment
Then you may qualify for a Certificate of Error.
Step 4: Gather Your Evidence Now
Whether you're appealing this year or next, start building your case:
- Research comparable properties in your neighborhood
- Document any property issues or needed repairs
- Take photos of your property's condition
- Save records of recent home sales in your area
- Review your property characteristics for errors
Run a free property analysis to see if you're overassessed and get a complete evidence package for your appeal.
Step 5: Set Up Monitoring for Next Time
Don't let this happen again. Sign up for property monitoring so you're alerted:
- The moment your next assessment is published
- When your township opens for appeals
- If comparable data changes that could support an appeal
- At every critical deadline
The Bottom Line
Missing your Cook County property tax appeal deadline is frustrating and expensive, but it's not necessarily catastrophic. You have options:
The key is to act quickly once you realize you've missed the deadline, and to make sure it never happens again by setting up proper monitoring and reminders.
Remember: The Cook County Assessor's office processes over 1.8 million properties. They make mistakes. If you don't catch those mistakes and appeal within the proper timeframes, you'll pay for their errors—literally.
Frequently Asked Questions
Q: I missed my deadline by just two days. Will they make an exception?
A: No. Cook County is strict about deadlines. There are no exceptions for being slightly late.
Q: If I wait until next year, will the appeal be harder?
A: Not necessarily. You can use the same evidence and comparable sales data. However, you'll lose a year of potential tax savings.
Q: Can I hire someone to appeal for me if I missed the deadline?
A: Property tax consultants are subject to the same deadlines you are. They can't file late appeals either, but they can help you determine if you qualify for a Certificate of Error or prepare for next year's appeal.
Q: Will appealing next year trigger a higher assessment?
A: No. Filing an appeal cannot result in a higher assessment in Cook County. The worst outcome is that your appeal is denied and your assessment stays the same.
Q: How much does property monitoring cost compared to what I could lose?
A: Our monitoring service costs a fraction of what you'd lose from a single year of overpaid property taxes. For most homeowners, missing one appeal opportunity costs more than several years of monitoring.
This article is for informational purposes only and does not constitute legal or tax advice. Property tax laws and deadlines can change. Always verify current deadlines with the Cook County Assessor's Office and the Cook County Board of Review.