Cook County's 2026 property tax reassessment on the South Side arrives after a cycle in which the county's machine-learning tax model made assessments fairer by one measure, yet homeowner bills soared. The appeals system, not the algorithm, is the culprit, according to a Forbes analysis of Cook County data [S1]. For South Side homeowners in neighborhoods like Bronzeville, the practical takeaway is that a fair valuation is only the opening offer; what a homeowner finally pays depends on who shows up to argue [S1].
The county's machine-learning model, built under former assessor Fritz Kaegi, estimated what a house would fetch on the open market and taxed it off that number [S1]. A 2025 evaluation by the University of Chicago's Center for Municipal Finance concluded that Kaegi's office had "dramatically reduced" the old regressivity that had overtaxed modest homes, and residential assessments sat inside the fairness range that the assessing profession sets for itself [S1]. Berry, a University of Chicago professor, estimated that the shift saved homeowners roughly $1.9 billion compared with what they would have paid under the old regime [S1].
Yet the model passed its own exam and the assessor who built it was shown the door. In the March 17 Democratic primary, Kaegi lost to challenger Pat Hynes, 52.5 percent to 47.5 percent, with no Republican in the race, meaning Hynes is all but certain to take the office [S1]. The thing that did Kaegi in was the very thing his model was supposed to cure: tax bills that kept climbing for the people who could least afford them [S1]. In West Garfield Park, the typical homeowner's property tax bill had just more than doubled in a single cycle, climbing 133 percent to $3,448, according to an analysis from the Cook County treasurer's office [S1]. A few miles north, in leafy Lincoln Park, the median bill nudged up by less than 6 percent [S1].
The appeals gap that shifts the burden
If the model is fair, why did bills go haywire? The answer sits at the Cook County Board of Review, a separate elected body that hears appeals after the assessor sets a value [S1]. The University of Chicago report found that commercial appeals there shift 3 percent to 4 percent of the tax base onto residential property every single year, effectively undoing the equity the assessor's office tries to build in [S1].
The treasurer's data tells the story in plain figures. Over the 2021 to 2023 reassessment cycle, a Chicago Sun-Times analysis of five years of bills found that businesses' tax bills dropped nearly 20 percent while residential bills rose more than 16 percent [S1]. Successful business appeals lopped $3.3 billion off commercial bills; homeowners' bills went up $1.9 billion [S1]. When the Magnificent Mile's office towers emptied out during the pandemic and won lower valuations, somebody had to make up the shortfall. That somebody was the family in West Garfield Park [S1].
Standout fact: Businesses challenged their assessments 64 percent of the time over the 2021-2023 cycle. Homeowners did so just 27 percent of the time, and that gap is where the tax burden quietly moved [S1]. In some affluent, well-lawyered pockets of the county, the appeal rate runs as high as 92 percent; in poorer neighborhoods it can sink to around 5 percent [S1]. A commercial owner keeps a tax attorney on retainer because the savings dwarf the fee. The owner of a $90,000 bungalow does not, and often does not even know the option exists [S1].
What this means for South Side homeowners
For homeowners in Bronzeville and across the South Side, the pattern is the same. A 2026 paper in Real Estate Economics by Junpeng Cai and colleagues examined Cook County records and found that commercial and industrial properties are more likely to appeal, more likely to win, and more likely to win larger reductions than small homes [S1]. The appeals process, the authors conclude, actively makes those commercial classes more regressive, not less [S1].
The finding has a long pedigree: a 2017 University of Chicago study reached the same verdict, that post-appeal assessments in the county come out more regressive than they went in [S1]. Build a fair number upstream, and the appeals layer downstream quietly bends it back [S1].
Kaegi spent the campaign pointing downstairs. "Bills went up because people were getting big cuts on commercial properties at the Cook County Board of Review," he said on the night he conceded [S1]. The Board fired back through commissioner Samantha Steele, who told Axios the cuts were necessary because the assessor had overvalued the properties to begin with. "It's time for the assessor to do the basic functions of the office and get the assessments right in the first place," she said [S1]. Two elected offices, each holding the other responsible, with homeowners stuck in the middle [S1].
The practical takeaway
If you own a home anywhere that reassesses property by computer, the practical takeaway is to find out whether you can appeal your assessment, and do it, because the people competing with you for a lower share of the tax bill almost certainly are [S1]. A fair valuation is only the opening offer. What you finally pay depends on who shows up to argue [S1].
The algorithm worked as designed. The system around it was designed to let some people opt out, and they did. That is not a software bug. It is a feature of how people are allowed to argue with the answer, and it is the part nobody has figured out how to fix [S1].
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