Cook County Property Tax Appeal: Complete 2026 Guide
Your property may be over-assessed. This guide explains how Cook County appeals work, what types of evidence the CCAO and Board of Review consider, and how self-filing works. TaxedTooMuch provides informational data only — filing, decisions, and any legal questions are entirely yours to handle.
2026 is Chicago's triennial reassessment year — the biggest appeal opportunity in a 3-year cycle. The Board of Review window is open now through May 31.
In this guide
How Cook County property tax appeals work
Cook County uses a triennial reassessment cycle— the county is divided into three groups (City of Chicago, North Suburbs, South Suburbs), and each group is reassessed once every three years. When your township is in its reassessment year, the CCAO issues updated assessed values. That's your primary appeal window.
Even in non-reassessment years, homeowners can appeal to the Cook County Board of Review — an independent three-member body that reviews assessments after the CCAO process closes.
The core principle: residential properties are assessed at 10% of estimated market value. If comparable homes are selling for significantly less than 10× your assessed value — or if similar nearby properties carry lower assessments per square foot — you have grounds to appeal.
Who should consider appealing
The data may support filing an appeal if any of the following apply to your property. TaxedTooMuch can show you the numbers — whether to file and how to proceed is entirely up to you.
- ·Recent comparable sales nearby suggest your home would sell for less than 10× your assessed value
- ·Similar neighboring properties are assessed at a lower rate per square foot than yours
- ·Your assessment increased significantly in the most recent reassessment year
- ·You purchased your home for less than 10× your current assessed value
- ·Your property has characteristics the assessor may have overweighted (condition, lot size, etc.)
The only way to know for certain is to look at the data. That's what TaxedTooMuch does — free for the initial comparison, $49 for the full data report.
Two appeal paths: CCAO vs. Board of Review
Cook County Assessor's Office (CCAO)
First-level appeals filed directly with the Assessor during your township's appeal window. Online filing, typically no hearing required for residential properties. Decisions within a few weeks. The CCAO focuses heavily on comparable sales evidence.
Cook County Board of Review (BOR)
Independent three-member body. Appeals open after the CCAO window closes for your township. If you missed the CCAO window, or are unhappy with the result, the BOR is your next step. The BOR weighs both comparable sales and uniformity evidence — and is where uniformity arguments tend to be strongest.
What evidence the CCAO and Board of Review consider
Both the CCAO and Board of Review evaluate two primary types of evidence:
Comparable Sales
Recent arm's-length sales of similar nearby properties. The CCAO prefers sales from the 12 months prior to January 1 of the tax year. This is the strongest evidence at both the CCAO and BOR levels.
Assessment Uniformity
Illinois law requires uniform assessment across comparable properties. If your neighbors carry lower assessments per square foot, that inequity is itself a valid appeal basis — no appraisal required.
Step-by-step: filing your Cook County appeal
- 1
Confirm your township and deadline
Your township is on your tax bill. Look up the current appeal window at our deadline calendar or directly at cookcountyboardofreview.com. Deadlines are firm — no extensions.
- 2
Find your Property Index Number (PIN)
Your PIN is a 14-digit number on your Cook County tax bill. You'll need it to file, and to pull your data on TaxedTooMuch.
- 3
Check your free comparison on TaxedTooMuch
Enter your address or PIN at taxedtoomuch.com/lookup. We show you how your $/sqft assessment rate compares to similar properties in the same CCAO neighborhood — free, instant.
- 4
Get your full data report
If the free check shows a potential over-assessment, the $49 PropFax report gives you a complete uniformity analysis: comparable assessed properties from your CCAO neighborhood, each with their building assessed value per square foot, and the gap between your rate and the neighborhood average — the data relevant to a uniformity appeal.
- 5
File online at the CCAO or BOR portal
Both portals accept online filings. Upload your evidence (typically a comp grid or the data from your PropFax report), enter your PIN, and describe your basis. No attorney required for residential appeals.
- 6
Track your decision and consider next steps
CCAO decisions typically arrive in 4–6 weeks. Board of Review decisions take longer. If granted, your assessment is revised. If denied at the CCAO, you can still escalate to the BOR — and from there to PTAB if warranted.
Frequently asked questions
What is the deadline to appeal my Cook County property tax in 2026?
Deadlines vary by township. The City of Chicago Board of Review window runs May 1–May 31, 2026. North and Northwest suburbs had earlier windows (January–March 2026). South and West suburbs are largely TBA. Always verify your township's specific deadline at cookcountyboardofreview.com.
Do I need a lawyer to appeal my Cook County property taxes?
No. Both the Cook County Assessor's Office (CCAO) and the Board of Review accept self-filed residential appeals. No attorney or tax agent is required. If you have questions about the legal aspects of your appeal, consult a licensed attorney or tax professional — TaxedTooMuch is not a law firm and does not provide legal advice.
What evidence do I need to appeal?
The two most accepted evidence types are comparable sales (recent arm's-length sales of similar nearby properties) and uniformity evidence (data showing similar nearby properties are assessed at a lower rate per square foot). You do not need an appraisal for a uniformity appeal.
How is property assessed in Cook County?
Residential properties in Cook County are assessed at 10% of their estimated market value. If your assessed value divided by 10% is higher than what comparable properties have sold for, you may have grounds to appeal.
What is the difference between a CCAO appeal and a Board of Review appeal?
The CCAO (Cook County Assessor's Office) handles first-level appeals, typically during the reassessment period. The Board of Review is an independent body that handles second-level appeals after the CCAO window closes. You can file both in the same year — a denial at the CCAO level does not affect your BOR case.
What does TaxedTooMuch provide?
TaxedTooMuch is an informational data service. We analyze your property using CCAO open data, identify comparable properties in your neighborhood, and generate a data report showing your assessed value per square foot versus the neighborhood average. We do not file appeals on your behalf and nothing we provide is legal advice.
About TaxedTooMuch (TTM)
TTM (TaxedTooMuch) is an informational data service. Not a law firm. Not legal advice. Not a tax advisor or appeal service. All estimates are for informational purposes only and do not guarantee any savings or appeal outcome. You are solely responsible for filing your own appeal, meeting all deadlines, and seeking any legal or professional guidance you may need. Appeal decisions are made exclusively by the CCAO or the Cook County Board of Review — not by TaxedTooMuch.
Dive deeper
Cook County Appeal Deadlines 2026 →
Township-by-township calendar — see what's open right now
How to Use Comparable Sales Data →
What makes a good comp and how to present it to the BOR
Uniformity Appeals Explained →
How the uniformity argument works and what data supports it
How Cook County Assessments Work →
Triennial cycles, the equalization factor, and how your bill is calculated
See if your property is over-assessed
Free initial check. Full data report for $49. The appeal deadline is coming.
Check my property — free