Data report · measured 4 July 2026
The Cook County Over-Assessment Report
We ran the reverse-comp engine across the entire public assessment roll. This is what the industry usually hides: how many Cook County homes are over-assessed, by how much, and how often an appeal actually wins.
How many Cook County homes are over-assessed?
How over-assessed are Cook County homes?
Measured across the public roll from 177,639 recent arms-length dwelling sales, projected onto the 1,062,512 Cook County dwellings we can assess. A home is counted as over-assessed when its assessment ratio sits materially above its neighbors’ median ratio.
About 124,000 Cook County dwellings are strongly over-assessed relative to comparable local properties — a conservative floor, measured only where nearby sales support the comparison.
| Over-assessment tier | Single-family | Condo | Total dwellings |
|---|---|---|---|
| Viable (≥10% above peer-median ratio) | 183,636 | 10,624 | 194,260 |
| Strong (≥15% above peer-median ratio) | 119,683 | 4,728 | 124,411 |
| Very strong (≥25% above peer-median ratio) | 57,884 | 1,466 | 59,350 |
Median achievable annual saving in the strong tier: $1,714 single-family, $809 condo. A conservative floor: it counts only dwellings with enough comparable local sales, and recently-sold homes get pulled toward their sale price, so the unsold majority is probably worse-assessed.
Source: ChonkHub reverse-comp engine, roll measured 4 July 2026.
How is “over-assessed” measured?
On the uniformity standard the appeal system itself uses. A dwelling is over-assessed when its assessment ratio — assessed value divided by market value — sits materially above the median ratio of its comparable peers. We estimated market value per dwelling by stratum from 177,639 recent arms-length sales, then compared each home’s ratio to its peer group.
Cook County’s dwelling universe is 874,659 single-family homes and 187,853 condos — 1,062,512 in all. The county-wide median ratio is about 8.5% for single-family and 9.2% for condos, near the statutory 10%. Homes well above their peers’ median are the over-assessment population.
How often do Cook County appeals win?
Appeals succeed far more often than homeowners assume, and the two stages compound. The tables below are the county’s own decision records — not our estimates.
Cook County Assessor — reductions by year
| Tax year | Appeals filed | Reduced | Median cut |
|---|---|---|---|
| 2021 | 373,644 | 31.9% | 10.6% |
| 2022 | 302,330 | 24.8% | 8.3% |
| 2023 | 243,425 | 21.4% | 8.5% |
| 2024 | 440,746 | 21.2% | 7.6% |
| 2025 | 362,528 | 16.2% | 6.8% |
Cook County Board of Review — reductions by year
| Tax year | Appeals filed | Reduced | Median cut |
|---|---|---|---|
| 2019 | 462,316 | 36.0% | 7.5% |
| 2020 | 384,626 | 28.5% | 8.2% |
| 2021 | 518,845 | 28.2% | 7.9% |
| 2022 | 469,007 | 28.4% | 7.1% |
| 2023 | 406,396 | 33.3% | 7.2% |
| 2024 | 571,841 | 39.4% | 5.5% |
Source: Cook County Assessor and Board of Review decision records, via the ChonkHub appeal database.
Why are so many homes over-assessed?
Mass appraisal values hundreds of thousands of parcels by formula. That is efficient at the county scale and inevitably wrong for individual homes, which land above or below their true comparable value. The homeowners who appeal correct their own figure; the ones who do not, over-pay — often for the full three-year cycle until the next reassessment.
That is the case for radical transparency. The data to know whether you are over-assessed is public. ChonkHub publishes it and hands you the tools to act on it, rather than charging a share of your savings to keep it opaque.
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