People assume a property tax assessment is a precise calculation done by someone who walked through their building and looked closely at every detail. In reality, most assessments are produced through mass appraisal, meaning a model applied across thousands of properties at once, not an individual evaluation of yours.

That matters more than most owners realize. Mass appraisal models are efficient, but efficient is not the same as accurate, and the data backs that up. Research on property tax appeals nationally shows that somewhere between 40 and 60 percent of appeals result in a reduction, which tells you a large share of assessments start out wrong in the first place. For commercial property in Illinois specifically, that number climbs even higher, with some studies citing a reduction rate above 70 percent on commercial appeals. Successful appeals typically reduce the assessed value by well over 7 percent.

Lake County's own numbers make the point even more directly…In the 2021 tax year alone, one property tax firm reported saving Lake County property owners a combined $46 million through successful appeals. That is one firm, in one county, in a single year. It should tell you something about how often the county's own assessments miss the mark.

It is also worth knowing that Lake County has one of the higher effective property tax rates in the state, at roughly 2.82 percent, well above the national average. On a Lake County property with a median market value, that works out to over $12,500 a year in property taxes. When the rate itself is already high, even a modest error in the assessed value turns into real money, year after year, until someone challenges it.

There is another wrinkle specific to commercial owners…Under Illinois law, corporate and LLC stakeholders cannot represent their entity at the Lake County Board of Review. An attorney is required. That is not a technicality designed to create business for law firms. It means that a lot of commercial owners either never appeal at all, or hand the process to any lawyer they can find quickly, without necessarily getting someone who actually specializes in how these assessments are derived, and where they tend to break down.

So what actually goes wrong in these assessments? In our experience, a handful of issues show up again and again…Vacancy and lost income never get factored in properly, even though an assessment is supposed to reflect what a building would actually sell for, given its occupancy. Deferred maintenance and physical obsolescence get overlooked, meaning an aging roof, outdated mechanical systems, or a layout tenants no longer want does not get reflected in the number. Sales comparisons lean on data that is stale or pulled from properties that are not truly similar, sometimes from a very different point in the market cycle. Properties get assessed in line with neighbors that look similar on paper but are not actually comparable once you dig into condition, use or income.

None of these errors are exotic. They are common, and they are the reason so many appeals succeed once someone actually takes the time to look. If your assessment has never been reviewed by someone outside the county's own process, there is a real chance that one or more of these issues is sitting in your property’s assessed value right now.

Ron Kingsley
Attorney at Law
Master of Laws in Taxation
Lake County Appeal


About the author

Ron Kingsley leads Lake County Appeal, one of the most successful property tax appeal firms in Lake County. He earned his Juris Doctorate from Loyola University of Chicago in the early 1980s, his Master of Laws in Taxation from DePaul University in the late 1980s and has run Lake County Appeal since 2014, with a focus on commercial property tax appeals.