Cook County home and business owners continue to face pressure from rising property values and tax bills. One way property owners can challenge an assessment they believe is inaccurate is by filing a property tax appeal.
Cook County has two primary ways to challenge an assessment: an appeal with the Cook County Assessor’s Office and a separate appeal with the Cook County Board of Review (BOR). Each has its own filing period, and deadlines vary by township. Understanding how to appeal, and when to file, can help property owners avoid missing an opportunity to challenge their assessed values.
The Cook County Assessor Appeal
Cook County homeowners and businesses face significant property tax challenges, but they have two opportunities to appeal their assessments through the county, compared with one in most other Illinois counties. The first appeal type is an assessor appeal, which is directly with the Cook County Assessor’s Office (CCAO). This is unique in Illinois, and often acts as the first chance to land a reduction or correction for taxes and values. While taxpayers in other counties can have informal meetings to request a reduction, only Cook has codified these into official hearings.
Many townships across the county have already seen these deadlines come and go earlier this year. Once a notice of reassessment is published, there are 30 business days for the people of a township to file an assessor appeal. These deadlines are staggered out, allowing the CCAO to process each township. If a taxpayer files an appeal and it is either rejected or insufficient, then they can file a follow-up appeal when the opportunity arises. If a taxpayer misses the initial deadline, they may also file for this second round of appeals.
Cook County Board of Review Appeals
These secondary appeals are filed with the Board of Review (BOR), which is an impartial body that acts as a referee between the CCAO and the taxpayer. In the rest of Illinois, the BOR appeal is the only mechanism that taxpayers have. BOR appeals are slightly more complex than assessor appeals, though they require similar evidence. If a taxpayer has already gathered information, facts, and evidence for an assessor appeal, much of this will still be useful for the BOR hearing, though it is good to have it better organized.
In recent years, something of a rivalry has occurred between the BOR and the CCAO. Each organization has blamed the other for out-of-control property values. Because of this, the BOR has developed a reputation for being much more favorable to taxpayers than it is to the arguments of the CCAO. Whether this is true or not can be debated; however, the sheer volume of appeals to the BOR cannot be denied. In 2025, a record number of protests were filed with the BOR, even for townships outside of reassessment. 2026 appears likely to surpass those numbers, as both homeowners and businesses seek to correct errors and challenge property values.
Shorter Deadlines
The filing periods for Cook County Board of Review appeals are township-specific and can be relatively short. Unlike the assessor’s appeal process, which generally allows 30 business days after the reassessment notice is published, BOR filing windows follow a separate schedule.
Because dates vary by township and tax year, property owners should check the official Board of Review calendar rather than rely on a general deadline. Preparing supporting evidence in advance can also help make the filing process more manageable.
Check the Cook County Board of Review’s official dates and deadlines for the current filing schedule.
Why Filing on Time Matters
While assessor appeals are an optional step in the property tax reduction process, the BOR deadlines are not. If a taxpayer fails to file by the deadline, they lose the ability to protest for the entire year. There is no way to retroactively protest either, so it is imperative that every taxpayer file on time if they wish to challenge their values. While a rare third deadline was opened in December of 2025, such an occurrence is rare, which means taxpayers should act as if these upcoming deadlines are the last chance. While appeals can be later escalated to the Property Tax Appeal Board (PTAB), this can only be achieved if a BOR protest was filed first.
How to Check Your Cook County Board of Review Deadline
Cook County Board of Review appeal deadlines vary by township. Some filing periods have already closed, while others may still be open.
Before filing, check the BOR’s official calendar to confirm your township’s opening and closing dates. If your township is not currently accepting appeals, review the county’s guidance for future filing opportunities.
Evidence Required by the BOR
We already have an article dedicated entirely to the evidence required for a successful BOR appeal, so we will do a brief overview. For a protest in Cook County to be successful, there must first be a valid ground for appeal. This is generally either overassessment or uniformity of assessment. Overassessment is when a property’s market value is much higher than what it would reasonably sell for on the open market. Unequal assessment occurs when a property is assessed at a higher value compared to neighboring properties .
Each ground for appeal has its own necessary evidence. For cases of overassessment, sales records dating back three years must be gathered to show the true market value for a property. For instances of lack of uniformity, assessments must be gathered from around the taxpayer’s home or business. These comparable properties, whether sales or assessments, must share as many commonalities as possible with the taxpayer’s property. These include size, location, age, the number of rooms, and other characteristics. This makes finding the right comparable properties the most important aspect of any BOR appeal.
O’Connor Gathers Key Evidence
Because of how specific the evidence needs to be for a successful BOR appeal, many taxpayers are discouraged by the task of gathering facts and comparable properties. Many have compared gathering evidence in Cook County to having a second job. O’Connor is here to guide you in this process and will provide expert support for this most important part of the process. We have been helping clients across the nation for over 50 years and know the evidence needed for your case.
When you sign up with O’Connor, we start by analyzing your assessment for any issues, mistakes, or incorrect values. This is done with data-driven techniques that we have refined over the decades. Then, we use our proprietary databases full of property sales, assessments, and more to identify the most appropriate comparable properties. These comparables will help tell the true story of your property, giving you a portfolio of evidence to prove your case. Finally, we coordinate your appeal with a law firm that specializes in property tax law. You will not be charged upfront for these services, and will pay only a portion of your savings if your taxes are lowered.
