March 25, 2026
The Cook County Assessor accepts appeals based primarily on comparable sales — recent sales of similar nearby properties. If homes like yours sold for less than your assessed value implies, you have a strong case.
Here's how to find and use comparable sales effectively.
The ideal comparable property is:
The more similar the comp, the stronger your argument.
Cook County Assessor's website — The Assessor publishes sales data publicly. You can search by PIN or address and see nearby sales.
Redfin, Zillow, Realtor.com — These aggregate MLS data and show recent sales with detailed information.
Illinois Tax Assessor data — Available through Overtaxed IL's free check tool, which pulls directly from county records.
Your appeal packet — Once you start an appeal, you typically need to submit 3-6 comparable sales as evidence.
In Cook County, the assessed value should be approximately 10% of market value. If comparable homes sold for $300,000, the correct assessed value would be around $30,000.
If your assessed value is $38,000 but comps suggest it should be $30,000, that's an $8,000 over-assessment — translating to roughly $1,000-1,500 in excess taxes per year depending on your tax rate.
Running comparable analysis manually takes hours. Overtaxed IL pulls comparable sales automatically when you run a free check.
Enter your address at overtaxed-il.com/check — we show your assessment alongside nearby comparable sales in 60 seconds. If there's a significant gap, we walk you through filing the appeal.