Cook County, Illinois · checked 11 October 2026

How to find comparables for a Cook County appeal

An appeal wins on evidence, and in Cook County the evidence is almost always comparables: similar homes that sold for less, or that are assessed lower than yours. Here's how to find good ones for free in about an hour.

Two kinds of comparable

Sales comparables show your home's market value is too high. If the Assessor's value for your home is $400,000 (an assessed value of $40,000 times 10) and three similar homes nearby sold for $350,000 to $370,000, that's a strong case.
Assessment (uniformity) comparables show you're taxed more than your neighbours. If similar homes on your block are assessed at $95 per square foot and yours is at $115, you can ask to be brought in line, even if your value is close to market.

You can use both in the same appeal, and many people do.

What makes a good comparable

Same neighbourhood. Ideally the same Assessor neighbourhood code (shown on your notice and the Assessor's property page), or within half a mile.
Same type. Same property class: a single-family home against single-family homes, a condo against condos in similar buildings.
Similar size and age. Within about 20% of your living area, built in a similar decade, similar style (ranch against ranch, two-storey against two-storey).
Recent and arm's length. Sales from the last one to two years, between unrelated people on the open market. Leave out foreclosures, short sales and family transfers.
Three to five of them. One cheap sale looks like cherry-picking; several that point the same way look like the market.

Where to find them for free

The Assessor's website. Look up your PIN at cookcountyassessoril.gov to see your recorded characteristics (square footage, bedrooms, age) and your neighbourhood code, then look up nearby homes the same way to compare assessed values.
Cook County's open data. The county publishes every recorded parcel sale in its "Assessor - Parcel Sales" dataset. You can filter by township and neighbourhood code and download the results.
Listing sites. Zillow, Redfin and Realtor.com let you filter recently sold homes on a map. Use them to find sales and photos, then confirm each sale's PIN and details on the Assessor's site.
Your own neighbourhood. A recent sale on your street that you know needed work, or that sold below asking, is often your best comparable.

Check your own record first

Before you look for comparables, check what the Assessor has on file for your home. A wrong square footage, an extra bathroom that doesn't exist, or a finished basement that isn't finished all push your value up. Fixing a wrong characteristic is the simplest appeal there is.

Presenting them

Make a simple table: address, PIN, sale date and price (or assessed value), square feet, age, bedrooms and bathrooms, and price per square foot.
Put your home in the first row so the reviewer can see the difference at a glance.
Add one or two sentences explaining what the comparables show, and attach photos of any damage or needed repairs in your home.
Upload it with your appeal at the Assessor (while your township is open) or the Board of Review.

Check if my home is over-assessed

Our free check takes the comparables you enter, adjusts them for size and shows the value they point to. See also Assessor deadlines and the Board of Review appeal.

Sources: Cook County Assessor, appeals, Assessor - Parcel Sales open dataset.