1 in 8 Cook County homeowners won a property tax reduction last year
Most coverage of property tax appeals reports how many people file. Almost nobody reports how many win. Cook County publishes enough data to answer that directly — and the answer is 189,430 residential parcels in 2025. Journalists: cite freely with a link.
The Cook County Assessor publishes three separate values for every parcel, every year: the mailed value the assessor first proposes, the certified value after the assessor's own review, and the board value after the Board of Review rules on appeals. Comparing the last two isolates exactly what the appeal process changes.
In 2025, that difference was about $639 million in residential assessed value — 1.18% of the certified residential total — spread across 189,430 parcels that ended below their certified value. Because Cook County assesses residential property at 10% of market value, that $639 million of assessed value corresponds to several billion dollars of market value taken off the rolls.
This is not a fluke year
Reductions at this scale have happened every year we can measure. The pattern holds through reassessment cycles, a pandemic year, and three different assessment levels:
| Year | Residential parcels | Certified value | After appeals | Value removed |
|---|---|---|---|---|
| 2025 | 1,587,854 | $54.06B | $53.42B | $639M (1.18%) |
| 2024 | 1,587,738 | $50.59B | $50.02B | $565M (1.12%) |
| 2023 | 1,586,914 | $47.13B | $46.72B | $414M (0.88%) |
| 2022 | 1,586,957 | $44.72B | $44.23B | $488M (1.09%) |
| 2021 | 1,585,866 | $41.62B | $41.13B | $492M (1.18%) |
| 2020 | 1,580,445 | $37.92B | $37.66B | $256M (0.67%) |
| 2019 | 1,580,364 | $41.20B | $40.67B | $524M (1.27%) |
The 2026 reassessment split Cook County in two
Cook reassesses on a three-year township cycle, and the 2026 values now on file cover 15 townships and 446,915 residential parcels. The result is not a countywide trend — it is a sharp divide. Seven west and southwest suburban townships saw residential assessed value rise 21% to 30%, while the other eight came in flat or slightly down. Total assessed value across all 15 rose just 2.6%, which hides the entire story.
| Township | Residential parcels | 2025 certified | 2026 proposed | Change |
|---|---|---|---|---|
| River Forest | 4,240 | $241M | $313M | +30.1% |
| Oak Park | 17,063 | $655M | $814M | +24.4% |
| Berwyn | 14,115 | $352M | $437M | +24.3% |
| Riverside | 5,902 | $211M | $260M | +23.2% |
| Palos | 20,501 | $608M | $744M | +22.3% |
| Stickney | 13,187 | $297M | $360M | +21.4% |
| Cicero | 14,521 | $316M | $382M | +20.9% |
| Lake View | 92,672 | $4436M | $4446M | +0.2% |
| West Chicago | 113,683 | $4431M | $4429M | -0.0% |
| Rogers Park | 20,474 | $604M | $601M | -0.4% |
| Maine | 49,269 | $1936M | $1911M | -1.3% |
| Norwood Park | 9,155 | $380M | $374M | -1.5% |
| Evanston | 22,072 | $1163M | $1142M | -1.8% |
| Elk Grove | 28,648 | $992M | $972M | -2.0% |
| New Trier | 21,413 | $2663M | $2600M | -2.4% |
What this means if you own a home
Two things follow from the data. First, appeals are not a long shot in aggregate — roughly 190,000 Cook County parcels were reduced in a single year, and filing costs nothing. Second, the reductions are concentrated among owners who actually filed, which is a small minority of homeowners. The value is there for people who ask for it.
Whether your specific home has a case depends on whether it is assessed above what comparable nearby sales support, whether it is assessed at a higher share of value than similar homes, and whether the county's record of your property is accurate. Our free check tests all three for any address in about two minutes and shows its sources, and the Cook County appeal guide walks through the township calendar and the forms.
Methodology
Computed on July 25, 2026 from the Cook County Assessor's Assessed Values dataset (Cook County Open Data, resource uzyt-m557), filtered to residential property classes (class codes beginning with "2"). Aggregates were produced with SoQL queries: parcel counts and the sums of mailed_tot, certified_tot, and board_tot grouped by year; the count of reduced parcels is the number of 2025 residential records where board_tot < certified_tot. The 2026 township table compares sum(mailed_tot) for 2026 against sum(certified_tot) for 2025 within the same township, restricted to the 15 townships that have 2026 values on file (446,915 residential parcels); it is a change in total township assessed value, not a median per-home change, and individual homes vary widely around it. Values are assessed values, not market values. "Value removed" is certified minus post-board value and reflects Board of Review outcomes; it does not include reductions the assessor granted earlier in the cycle, so it is a conservative measure of what challenging an assessment achieves.
Journalists and researchers: cite freely. We'll run custom cuts — by township, neighborhood, or property class — on request at hello@grovehopper.com. Related: our full-population analysis of Philadelphia's 2027 reassessment.