We matched 26,310 Cook County house and townhouse sales from 2024 to the Assessor's values for tax year 2025. The cheapest tenth of those sales, under $170,000, carried a median Assessor value equal to 93% of the sale price. Across all the sales, the median was 89%.
That looks like cheaper homes are assessed higher. But more than half of the sales in that cheapest tenth had a company as the buyer or the seller. Leave those sales out and the cheapest tenth falls to 86%, below the 89% median.
The bigger story for a homeowner is not your price band. It is how far your own home sits from similar homes near you.
Quick Answer
Only a little, and not in a steady line. In our tax year 2025 test, the cheapest tenth of house sales was assessed at 93% of price against 89% overall, but much of that gap came from sales involving companies; without them it was 86%. In every year we tested, the cheapest tenth sat above the next tenth up. Within each region in the year it was reassessed, the cheapest and most expensive fifths of sales were within a few points of each other. Between reassessments, gaps open up as prices move unevenly. After Board of Review appeals, expensive homes ended up a bit lower relative to price than cheaper ones. For your home, the useful test is your own value against similar nearby sales.
How we measured it
The measure is simple: the Assessor's market value divided by the sale price. A home that sold for $300,000 with an Assessor value of $270,000 has a ratio of 90%.
- Values: the Assessor's tax year 2025 values, as first mailed and after the Board of Review. For homes, the Assessor's market value is the assessed value times 10.
- Sales: calendar 2024 sales, the year just before the January 1, 2025 valuation date.
- Screens: one-parcel sales only, the Assessor's own sale filters, and the deed types its model uses. We also dropped foreclosure, court and estate deeds, and sales with a bank or government agency on either side. Extreme ratios were trimmed with the standard rule in the Assessor's ratio-study code.
The details are in "The numbers behind this article."
The countywide picture, tax year 2025
Median Assessor value as a share of the 2024 sale price, by tenth of sale price:
| Price tenth | Sale price | Assessor value | After Board | Without company sales | Company on either side |
|---|---|---|---|---|---|
| 1 | under $170,000 | 93.3% | 92.5% | 85.8% | 54% |
| 2 | $170,000 to $235,000 | 77.6% | 77.3% | 79.0% | 36% |
| 3 | $235,000 to $279,000 | 80.0% | 80.0% | 81.6% | 28% |
| 4 | $279,000 to $316,000 | 83.6% | 83.3% | 84.2% | 21% |
| 5 | $316,000 to $355,000 | 85.7% | 85.3% | 86.1% | 19% |
| 6 | $355,000 to $402,000 | 89.1% | 88.2% | 89.2% | 17% |
| 7 | $402,000 to $467,500 | 92.0% | 90.9% | 91.8% | 15% |
| 8 | $467,500 to $590,000 | 92.0% | 90.1% | 92.0% | 14% |
| 9 | $590,000 to $862,000 | 93.1% | 90.8% | 93.2% | 15% |
| 10 | over $862,000 | 94.5% | 91.3% | 93.9% | 19% |
Three things stand out.
The bottom tenth is a small bump. It sits well above the second tenth, and more than half its sales involve a company. Without those sales it is still above the second tenth, but below the county median.
Above the bottom tenth, the share rises with price. That is mostly geography. The north suburbs were reassessed for tax year 2025, so their values were fresh, and they hold many of the county's pricier homes. City and south suburban values were set in earlier years and had fallen behind 2024 prices.
The Board round trims expensive homes more. After appeals, the top tenth dropped 3.2 points, from 94.5% to 91.3%. The bottom tenth dropped 0.8 points. We saw the same tilt in tax years 2023 and 2024.
Each region in its reassessment year
When values are fresh, price bands sit close together. Median Assessor value (as first mailed) as a share of price, by fifth of sale price:
| Region and tax year | Sales | Cheapest fifth | 2nd | 3rd | 4th | Priciest fifth |
|---|---|---|---|---|---|---|
| City, 2024 (2023 sales) | 8,246 | 94.7% | 92.0% | 92.3% | 93.1% | 96.6% |
| North suburbs, 2025 (2024 sales) | 8,045 | 95.7% | 95.5% | 96.2% | 96.7% | 97.4% |
| South and west suburbs, 2026 (2025 sales) | 8,872 | 94.4% | 92.0% | 92.9% | 92.7% | 94.4% |
The 2026 row uses first mailed values, because Board values for tax year 2026 were not final when we ran the numbers.
In all three, the cheapest fifth was assessed at the same share as the priciest fifth or lower.
Between reassessments, the gaps move
Values are reset only once every three years. In between, prices keep moving, and not evenly.
- North suburbs, tax year 2024 (values from the 2022 reassessment, 2023 sales): the cheapest fifth sat at 88.8% and the priciest at 76.6%. Here cheaper homes really were assessed at a higher share.
- City, tax year 2025 (values from the 2024 reassessment, 2024 sales): the second-cheapest fifth, roughly $209,000 to $292,000, sat at 72.3%, the lowest of any band. Those homes sold for well above their values.
So whether cheaper homes look over-assessed depends on where your region is in the three-year cycle, and on how prices moved in your part of it.
The gap that matters more: your home versus your neighbors
Price bands are averages. Individual homes vary far more.
In our tax year 2025 test, 15.6% of the homes that sold had a ratio at least 20% above the median for their region. Excluding sales involving companies, it was 12.3%. In the freshly reassessed north suburbs it was 5.9%. In the city it was 21.2%.
That spread is what an appeal can fix. If your assessment is higher, relative to value, than similar homes nearby, that is a uniformity argument. If your value is higher than what your home would sell for, that is an overvaluation argument. Our guide to overvaluation versus lack of uniformity explains both.
A countywide band average is not evidence for your home. Comparable homes are.
What to do with this
- Find your Assessor market value: the assessed value on your notice times 10.
- Compare it with three to five recent arm's-length sales of similar homes nearby: same class, size, age and construction.
- Compare your assessment per square foot with similar homes on your block or in your neighborhood.
- If yours is clearly higher on either test, file inside your township's window. County forms are free.
One practical point for lower-priced homes: sales near them more often involve companies (54% in the cheapest tenth, against 14% to 19% in the top half), so sale prices nearby can be uneven. A clean, arm's-length sale of a similar home near you can carry real weight.
Where Censum fits
On Censum's free appeal check you enter a PIN or address and see appeal odds for your home, built from past Board of Review outcomes on similar homes, plus the appeal window that is open. Censum prepares appeal packets if you want help. The Board decides every appeal.
The numbers behind this article
Censum's tabulation, run November 11, 2026, joining the Cook County Assessor's Parcel Sales dataset (wvhk-k5uv) to its Assessed Values dataset (uzyt-m557) by PIN. Houses and townhouses are classes 2-02 to 2-10, 2-34, 2-78 and 2-95. Sales screens: sale date in the calendar year shown; one parcel, not part of a multi-parcel sale; the dataset's three sale filters all false (same price within 365 days, under $10,000, quit claim or executor or beneficiary deed); deed type Warranty, Trustee or Other; state transfer-declaration deed types for judicial, sheriff's, tax, foreclosure, court officer, executor, administrator, guardian and conservator deeds removed; sales with a bank, mortgage company, federal housing agency, city, village, county, sheriff, land bank or relocation company on either side removed; same-name buyer and seller removed; last sale kept when a PIN sold twice; the value-year class had to match the sale class. Ratios more than three interquartile ranges outside the quartiles were trimmed within each region, the default rule in the Assessor's open-source ratio-study package. "Company" means the buyer or seller name contained LLC, Inc, Corp, Company, Holdings, Properties, Investments, Capital, Ventures or Group. Tax year 2025: 54,184 one-parcel residential sales passed the dataset's own filters, and 26,310 house sales remained after our screens. Regions follow the Assessor's three groups (City, North, South). We also ran the two standard fairness tests the Assessor's package computes. The Assessor's countywide house values, as first mailed, fell inside the accepted ranges for both tests in every year we tested (tax year 2025: price-related differential 0.986, price-related bias 0.047). A same-year check, tax year 2025 values against 2025 sales, showed the same shape.
FAQ
Does the Assessor assess cheaper homes at a higher share of value?
In our tests, a little, at the very bottom of the market. The cheapest tenth of sales sat above the next tenth in every year we tested, partly because of sales involving companies. Within freshly reassessed regions, price fifths were within a few points of each other.
Why are most ratios below 100%?
Values reflect January 1, and prices kept rising. Regions not reassessed that year also carry older values. Tax rates are spread over everyone's values, so what matters for your bill is your ratio compared with other owners.
Is "my home is cheaper" a basis for an appeal?
No. The Board looks at your home. Use comparable sales or the assessments of similar nearby homes.
Do Board of Review appeals change the picture?
A little. After the Board round, the most expensive tenth of homes fell about 3 points relative to price; the cheapest tenth fell under 1 point.
What year pairing did you use?
Tax year values against sales from the calendar year before, the window closest to the January 1 valuation date.
Sources
- Cook County Assessor, Parcel Sales dataset (Cook County open data)
- Cook County Assessor, Assessed Values dataset (Cook County open data)
- Cook County Assessor, residential valuation model documentation (sales screens, valuation date)
- Cook County Assessor, assessr ratio-study package: outlier rule, PRD and PRB
- Cook County Assessor, Definitions for the Classifications of Real Property (10% level for residential)
- Cook County Assessor, Assessment and Appeal Calendar (three-year cycle)
- Cook County Assessor, 2026 Guidelines for Filing Appeals (choosing comparable properties)
Sources accessed November 11, 2026.
Next step
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Censum LLC is a data and analytics company, not a law firm and not a tax advisor. Censum is independent and is not affiliated with Cook County or any government agency.