Cook County appeal evidence
How to find comparable sales for a Cook County property tax appeal
A useful comparable sale is not simply the cheapest nearby property. It is a recorded sale of a property that resembles yours closely enough to make the price meaningful evidence.
By Check the County, operated by Embento LLC. Updated . This is general public-record research information, not legal, tax or appraisal advice.
For a map-based walkthrough, see how to use CookViewer to compare properties.
Recently bought the home you want to appeal? Read our guide to a Cook County property tax appeal after buying a home before comparing other sales.
Verify your property record first
Before searching for sales, check the Assessor's record for your property. Confirm its assessment neighborhood, property class and type, building size, age, lot characteristics and other relevant facts. If the starting facts are wrong, a search based on them can produce poor comparisons.
Keep the property type consistent. Do not mix a single-family home with a two- to six-flat or a condominium. Those are different types of property and should not be treated as interchangeable sales evidence.
What makes a sale comparable?
Look first within the same assessment neighborhood and property class or type. Then compare building size, age, lot characteristics and how recently each property sold. No one characteristic decides the answer; the closer the overall match, the easier it is to explain why the sale is relevant.
Price alone is not enough. A low-priced property may be much smaller, older, on a different lot, or unlike your property in another material way. A sale can be nearby and still be a weak comparable.
Check whether the sale itself is unusual
A family transfer, distressed transaction or sale of a heavily renovated property may not reflect the same market circumstances as an ordinary sale of a similar home. Review the public record and the property facts you can verify before relying on an unusual transaction.
If you cannot confirm why a sale is unusual, do not guess. Describe only what the records support and follow the receiving office's current evidence instructions.
A hypothetical comparable-sales review
Every property, transaction and number in this example is fictional. These are research decisions for this exercise, not sales the county has accepted, a CheckTheCounty eligibility result, or an appraisal.
Suppose you are reviewing a 2026 assessment with a January 1, 2026 valuation date. The fictional subject is a 1,600-square-foot, single-family brick ranch built in 1960, on a 6,000-square-foot lot. Its county estimated market value is $360,000. Assume the subject record and its condition at that date have been verified.
The example uses 2025 sales. Follow the receiving office's current instructions for relevant evidence; these dates and property differences are not universal admissibility rules or numeric tolerances.
| Candidate and assumed records | Decision for this exercise |
|---|---|
| A: $320,000 on August 15, 2025 1,600 sq ft; built 1960 | Retain for review. Same assessment neighborhood and single-family class, brick ranch, 6,000-sq-ft lot and similar condition. Assume the recorded sale and ordinary market circumstances are documented. |
| B: $346,500 on June 20, 2025 1,650 sq ft; built 1961 | Retain for review. Same neighborhood, class, style and lot size; similar condition. Assume documented market-sale circumstances. Note the additional 50 sq ft instead of pretending the homes are identical. |
| C: $372,000 on October 10, 2025 1,550 sq ft; built 1958 | Retain for review on the same assumed neighborhood, class, style, lot, condition and sale verification. Its higher price is not a reason to discard it. Record the size and age differences. |
| D: $260,000 on July 1, 2025 900-sq-ft condominium | Reject as a single-family comparison in this exercise. A different property type and ownership setting are material differences, even if it is nearby and cheaper. |
| E: $275,000 on September 5, 2025 1,600-sq-ft ranch | Reject as ordinary market-sale evidence in this exercise: assume documents establish a below-market transfer between relatives. Similar physical facts alone do not resolve the sale circumstances. |
| F: $310,000 on May 9, 2025 1,600-sq-ft ranch | Hold for verification. The document reference or transfer circumstances cannot be confirmed. Missing information is not proof of a bad sale, and it is not proof of an ordinary market sale. |
Work through the arithmetic without overstating it
A's sale price per building square foot is $320,000 ÷ 1,600 = $200. B is $346,500 ÷ 1,650 = $210; C is $372,000 ÷ 1,550 = $240. The median of those three ratios is $210 per square foot. These are unadjusted sale-price ratios, including the land in each sale price.
That calculation does not establish the subject's value or an assessment reduction. The retained prices span $320,000–$372,000, including a sale above the subject's $360,000 county market value. Review the differences and any supported adjustments; do not invent dollar adjustments, drop C to lower the result, or compare these sale-price ratios with building-only assessment ratios.
In a real file, keep the PIN, recorded document reference, sale date and price, sources, characteristic year, and notes about condition at the relevant time. Later property records may describe renovations or other changes that were not present when a home sold. Explain missing historical information.
Blank comparable-sales research worksheet
Print this page or copy these prompts into your own notes. Repeat the candidate section for each sale you investigate, including rejected and unresolved candidates. This is an optional preparation aid, not a county form, appraisal, or filing submission.
Subject property and filing context
- PIN/address, township and assessment neighborhood: ____________________
- Assessment/tax year, valuation date and receiving office: ____________________
- County market value and assessment stage (keep assessed value separate): ____________________
- Class/type, style, building area, age and lot area: ____________________
- Condition at the valuation date; source and characteristic year: ____________________
- Complaint deadline, evidence deadline and official source checked on: ____________________
Candidate sale — repeat as needed
- Candidate PIN/address, neighborhood and class/type: ____________________
- Sale date, recorded price and document reference: ____________________
- Sale source/link and date checked; transaction circumstances verified by: ____________________
- Building area, style, age, lot and condition; source and characteristic year: ____________________
- Differences from subject and any missing historical information: ____________________
- Unadjusted sale price ÷ building sq ft (if area is verified): ____________________
- Any proposed adjustment and supporting evidence, or none: ____________________
- Retain / reject / hold; reason and unresolved questions: ____________________
Use the complete research record to explain your choices. A filled worksheet does not mean the evidence qualifies for a paid guide or that an appeal will succeed.
Do not confuse two per-square-foot measures
Comparing your bill with a neighbor's? Our guide to why a neighbor’s property taxes may be lower separates assessment comparisons from exemptions and includes a worked example.
Sale price per square foot divides a recorded sale price by building area. Assessed value per square foot divides an assessed value by building area. They answer different questions and should not be compared as though they were the same measure.
What if there are few recent sales?
Use the closest supportable matches available without mixing property types or hiding important differences. Review the county's current instructions, explain relevant limitations in the evidence, and avoid overstating what a small or imperfect set of sales proves.
Find your township guide for local context, or start with the broader Cook County property tax appeal research guide.
Official filing resources
Official references for this example: the Assessor's comparable-property guidance addresses neighborhood, class, size and age. The BOR's archived pro-se guide describes similar recent sales; follow the current BOR rules for your filing. The hypothetical screening choices above are explanatory, not county rulings.
Before comparing values, use our assessment notice walkthrough to distinguish the county's estimated market value from assessed value.
Ready to organize your findings? Use the printable appeal evidence checklist to prepare your documents and record filing confirmations.