Choosing comparables for a Cook County appeal

What a comparable is, and why it matters

A comparable (or "comp") is a home similar to yours. The Assessor's office says comparable homes should have similar market values, and therefore similar assessed values.

If similar homes near you are assessed lower than yours, you can argue "lack of uniformity." That is one of the most common grounds for a homeowner appeal at both the Assessor and the Board of Review.

Comps can also be recent sales. A sales-based argument says your home is worth less than the Assessor's estimate because similar homes sold for less.

What has to match

The Assessor says two homes must be similar in location (township and neighborhood), property class code, age, building square footage and land square footage. Its 2026 appeal guidelines list the seven factors analysts care about most for homes:

• Proximity. Analysts look for the closest comps, not the lowest-valued ones.
• Building square footage. Similar in size to your home.
• Age. Similar in age.
• Exterior construction. Masonry with masonry, frame with frame.
• Basement. Slab, crawl, unfinished or finished, like yours.
• Land square footage. Similar lot size.
• Garage. Attached or detached, and the same number of cars.

The Board of Review adds that comps should preferably be on your own block, may be a block or two away, and must be within your neighborhood. Its example: if your home is class 2-03 (a small ranch or bungalow), your comparables should be 2-03s too.

Same class code is not enough

The Assessor gives this example. Your home is in neighborhood 40, class 203, 1,600 square feet and 22 years old.

PIN 2 has the same neighborhood and class, but it is far smaller and much older, so it is not a fair comparison. The Assessor's residential appeals page adds that if you submit homes that are very different from yours, they will not be considered as comparables.

How many comps, and what to include

• Assessor: its rules ask for at least 3 comparable properties, recommend at least 5, and require the PIN of each. The SmartFile comparables tool lets you add up to 5; the Assessor's Cook Viewer instructions also allow attaching up to 6 comparable PINs as files.
• Board of Review: it suggests 3 to 5 similar properties, with addresses, PINs, assessed values (land, building and total) and photos, for your home and each comp. A photo of the front of your own home is required; photos of comps are strongly encouraged.
• PTAB (later stage): asks for at least three comparables from your neighborhood with all relevant data, such as property record cards.

At the Assessor, an owner filing for their own residence does not have to include photos. Every filer must still list a PIN for each comp.

Compare per square foot

Big and small homes naturally carry different assessments, so compare them per square foot. The Board of Review's formula: building assessment divided by building square footage equals building assessment per square foot.

Here is a made-up example to show the math (not real properties):

The comps fall between 13.00 and 14.00 per square foot, with a middle value of 13.50. At 13.50, your 1,600 square feet would carry a building assessment of 21,600 instead of 24,000. That is the argument you would make; the county decides whether to accept it.

For context, residential assessed value in Cook County is 10% of the Assessor's market value estimate, per the Cook County Clerk's tax rate report formulas.

Don't cherry-pick

The Assessor's rules tell filers to refrain from "cherry picking" only the comps that are lower in value than their home. Its guidelines note that software makes picking only the lowest values easy, and that analysts want the closest, most similar homes instead.

The Board of Review also says it is required by law to consider what homes in your neighborhood have been selling for. A list of oddly low comps that ignores recent sales is unlikely to persuade anyone.

Small extras matter less. The Assessor says that unless a home is truly unique, it is not overly concerned with sheds or swimming pools.

Using sales as comps

For a sales argument, each sale should be an arm's-length transaction at fair market value. The Assessor's rules exclude distressed sales and sales between related people.

The Board of Review accepts similar homes sold within the last 3 years as evidence that the Assessor's value is too high. If you bought your own home in the past 3 years for less than the Assessor's market value, your closing documents can be evidence too.

Where to find comps for free

• Cook Viewer (Cook County GIS map): find your property and click "Compare this Property." The Assessor recommends it because it automatically filters by neighborhood, class, square footage and age.
• SmartFile Comps Grid, built into the Assessor's online appeal.
• The Assessor's Home Value Report and Housing Market Tracker.
• Your community newspaper, which the Assessor says lists properties in your neighborhood a few days after notices arrive; your notice names the paper and date.

Our free check of your home against similar homes runs a first pass for you. If the numbers point to an appeal, the optional document packet ($49, refunded if the county says no) lays out your comps for the forms, and you file it yourself, free, on the county site.

Do you even need comps?

At the Assessor, no. Its residential appeals page says you do not need to file a list of comparables, because its analysts review similar homes themselves. Good comps still make your reasoning clear.

At the Board of Review, the Board says a well-documented, orderly case gives you a much better chance at a reduction, and its staff can help you find comps. For the full process, see how to appeal step by step and Assessor vs Board of Review.