Understanding Market Value vs. Assessed Value in Cook County
Updated June 16, 2026
If you’ve ever looked at your property tax bill and wondered how the County came up with that number, you’re not alone. Many Cook County homeowners are confused by the difference between “market value” and “assessed value.” These two terms sound similar but have different meanings, and understanding them can help you determine whether you’re being taxed fairly.
I help Cook County property owners make sense of the assessment system and appeal valuations that come in too high. Here’s what you need to know about how market value and assessed value work, and how they affect your property taxes.
Market Value: What Your Property Could Sell For
Market value is what your property would likely sell for in today’s open real estate market. The Cook County Assessor’s Office defines market value as the estimated price your property would bring in a fair sale between a willing buyer and seller.
This estimate is based on data such as:
- Recent sales of similar properties in your neighborhood
- Location and size of your home
- Condition and age of the property
- Market trends and neighborhood changes
The Assessor’s Office updates property values on a three-year reassessment cycle, township by township. Every three years, your property’s market value is reviewed based on the most recent sales data and local trends. You’ll receive a Reassessment Notice showing the County’s new estimate of your market value.
Assessed Value: The Number That Determines Your Tax Bill
Assessed value is the number used to calculate your property taxes. It’s a percentage of your property’s market value, not the full amount.
In Cook County:
- Residential properties (Class 2) are assessed at 10% of market value
- Commercial and industrial properties (Class 5) are assessed at 25% of market value
For example, if the Assessor estimates your home’s market value at $300,000, your assessed value would be $30,000 (10% of $300,000). The State of Illinois then applies an equalization factor to that figure to reach your Equalized Assessed Value (EAV). Any exemptions you qualify for come off the EAV, your local tax rate applies to what’s left, and that’s your bill. I always tell clients to confirm their exemptions actually show up on the bill, because that’s some of the easiest money to leave on the table.
Common Mistakes in Property Assessments
The Cook County Assessor’s Office uses a mass appraisal system to estimate values. While this helps process hundreds of thousands of properties efficiently, it can lead to errors. Factors like outdated data, incorrect property details, or poor comparable sales can all result in inaccurate assessments.
When that happens, property owners often find that their “market value” is higher than what their home could realistically sell for, or that their home is overassessed compared to a nearly identical neighbor’s home. This inflated value leads to an unfairly high assessed value and a bigger tax bill. In my experience that gap, the difference between what your record says and what comparable homes actually show, is often the very thing that wins an appeal.
How to Review Your Property’s Assessment
You can review your property’s information and assessed value online. Look up comparable properties in your neighborhood to see how your assessment compares to similar homes.
If you believe your property’s market value is higher than it should be, or if your property details are incorrect, you have the right to appeal your assessment.
What You Need to File an Appeal
When you file an appeal, you’re challenging the County’s estimate of your property’s market value. To properly prepare your appeal, you may need evidence such as:
- Recent sales data from similar homes in your area
- Photos showing your property’s condition
- A professional appraisal
- Assessment data from comparable properties
Appeals must be filed within the open filing period for your township, usually within 30 to 45 days of receiving your reassessment notice. Missing that deadline means waiting until your next appeal window opens.
Getting Professional Help with Your Appeal
While anyone can file an appeal, the process can be detailed and time-sensitive. Many homeowners lose out on savings because they don’t present the right evidence or follow all filing rules.
That’s exactly what I do as a Cook County property tax attorney: gather and present the market data, identify genuinely comparable properties, and make sure your evidence meets the Assessor’s standards. I bring 12+ years of legal experience to that work, including years handling administrative-law cases for the City of Chicago, and appeals at the Assessor and Board of Review run on that same strict, ordinance-driven footing.
My firm focuses on Cook County property tax appeals. I can help you determine whether your assessed value actually reflects your true market value, and if it doesn’t, guide you through the appeal.
Know the Difference and Protect Your Wallet
Market value and assessed value are closely connected, but they’re not the same. Your market value reflects what your property could sell for, while your assessed value determines how much you pay in taxes.
Understanding this difference is important because it shows you exactly how your tax bill is calculated. When the Assessor gets your market value wrong, it directly inflates your assessed value and costs you money every year.
If you suspect your assessment doesn’t match reality, don’t wait for your next tax bill to find out. Review your property’s assessment annually and compare it to similar homes in your area. If something looks off, you have the right to challenge it.
Contact my office today for a free review of your current assessment and find out whether an appeal could lower it.
