A Chicago family was shocked by a $24,000 property tax bill — a 300% spike from their last payment cycle. What went wrong?

"I thought it was absolutely insane," his daughter Whitney told CBS News Chicago. (1) "How could you go up 300%?"

Two neighboring properties got hit, as well, although they didn’t have it quite as bad as the Castle family. The Cook County Assessor's Office did not respond to CBS’s requests for comment. But Pat Hynes, who just won the Democratic primary to become Cook County's next assessor, said he thinks he knows what caused it.

The error hiding in the land value

Hynes, who used to work as a field inspector for the Cook County Assessor's Office, says a home’s value assessment is split into two — the building, itself, and the land.

If the value of the land is suddenly and incorrectly inflated, the overall assessment — and the tax bill — can increase dramatically, even when nothing has been done to the house.

Hynes, who dealt with a cluster of land assessment errors in 2024, says the pattern was familiar. The county assessor did an assessment in 2021 and also in 2024.

“Obviously, the market did not go up 300% in three years,” Hynes told CBS (1). “And so, there's an error when it doesn't follow the market.”

Hynes also said the Cook County Assessor's Office used to run a Tech Review department to spot odd or obviously wrong property‑value assessments before they turned into final tax bills.

"That audit function, really, doesn't exist anymore, and really would be useful to sort of catch these kinds of errors before they become the taxpayer's problem," he said (1).

Hynes says he’ll like to reinstate the Tech Review department to check these kinds of outliers.

Why this isn't a one-family problem

Cook County funds local services through property taxes, and the county collects a fixed amount of tax from property owners for this.

For example, the county taxes commercial buildings (The Loop) — Chicago’s downtown area for office buildings and landmarks — and residential homes. But after the COVID-19 pandemic, downtown office buildings started losing tenants. Empty offices are worth less, and their owners appealed their assessments at the Board of Review to reflect that.

The median tax bill for The Loop dropped from $14,942 to $10,709 (2) in a single cycle, which means the county now collects less from commercial properties.

But since the county still needs the same amount of money to fund local services, the burden automatically shifted onto residential homeowners, especially on the south and west sides.

The median Chicago homeowner's bill rose (3) 16.7% to $4,457 — and in some south- and west-side neighborhoods, it was more than that. West Garfield Park's median bill rose 133%. North Lawndale, 99%. Englewood, 82.5%. And these are medians — which means plenty of individual households in those areas saw bills far higher than that.

"When the Loop gets a cold, the rest of the city gets pneumonia," Cook County Treasurer, Maria Pappas, said in a press release. (4)

What Cook County homeowners can do right now

If your bill looks wrong, the appeals process is free — and more accessible than most people realize.

Start with the Cook County Assessor's Office. (5) File online through the online portal, SmartFile, which will require your Property Index Number (PIN). (6) The appeal window opens by township on a rolling schedule, so check your specific deadline. (7) The Assessor reviews your filing and typically issues a decision within a few weeks.

If the reduction isn't enough — or if you want a second opinion — file with the Cook County Board of Review, an independent quasi-judicial body that operates separately from the Assessor. (8)

You can file with the Board even if the Assessor already gave you a partial reduction, and even if you never filed with the Assessor at all. (9) Around 55% of Board of Review appeals result in a reduction. (10)