Research
How Illinois assessments are built, where they go wrong, and what an owner can actually do about it. 105 articles, written to be useful to somebody who then does it themselves.
How many homes are over-assessed? We measured it in two states
We compared every property against its closest neighbours in Illinois and Connecticut. About 1 in 12 sits far enough above its peers to be worth an appeal, and the median gap is 22%.
Research · 4 min
What Connecticut's statewide assessment data shows
Connecticut publishes every town's assessment roll in one place, at a flat 70% ratio with no equaliser. That makes it the easiest state in the country to check whether your assessment is fair.
Research · 3 min
The county's record of your house is often wrong, and that is your best appeal
Building areas recorded as lot sizes. Years built with two years run together. What we found loading millions of property records — and why a record correction beats a uniformity appeal.
Research · 3 min
When not to appeal your property taxes
Most advice tells you to always appeal. The county's own data says otherwise. Six situations where filing is a waste of an evening, and what to do instead.
Research · 3 min
How property tax assessment actually works, end to end
From the assessor's valuation model to the number on your bill: every step, what can be disputed at each one, and where most homeowners misunderstand the process.
Research · 4 min
The deadline is the most common reason people lose their appeal
Property tax appeal windows are short, staggered by township, and absolutely unforgiving. How the calendar works in Illinois and Connecticut, and how to never miss it again.
Research · 3 min
Property tax appeal success rates for all 38 Cook County townships
An appeal in Jefferson Township succeeded four times as often as one in Palatine in the same year. The full table, from the Assessor's published decisions.
Research · 3 min
How we count: the method behind every number on this site
Where the data comes from, what we exclude and why, the mistakes we made and corrected, and how to check any of it yourself.
Research · 4 min
What a winning property tax appeal is actually worth
Across 408,796 successful Cook County appeals, the median reduction was 8.4% of assessed value. Here is what that means in dollars, and whether it is worth your evening.
Research · 3 min
Property tax appeals got much harder to win between 2021 and 2025
The Cook County success rate roughly halved in four years, from 31.9% to 16.2%, while the number of appeals stayed high. What the data shows, and what it does not explain.
Research · 3 min
Do property tax appeals actually work? We counted 1,807,534 decisions
Appeal services advertise success rates above 80%. The Cook County Assessor publishes every decision it makes. We counted them: 23%.
Research · 7 min
Three words on your decision letter tell you whether you won
The Cook County Assessor's reasons follow a pattern nobody documents. "This is due to" is a denial 100% of the time. "This is the result of" is a reduction 98.4% of the time.
Research · 6 min
Does hiring someone to appeal your property taxes help? Six years of data say it is not settled
Attorneys and agents commonly take a third of the first year's saving. Across 1.79 million Cook County decisions, the advantage over filing yourself changes sides from year to year.
Research · 5 min
The property tax exemptions nobody tells you about, in all 51 jurisdictions
An appeal argues about what your home is worth and might win 8%. An unclaimed exemption is money you are entitled to by statute, granted without argument, and often worth more.
Research · 7 min
Your assessed value is not your home's value, and the gap is the point
Cook County assesses homes at 10% of market. The rest of Illinois uses 33⅓%. Connecticut uses 70%. Confusing these is the most common reason an appeal goes nowhere.
Research · 5 min