When the Chicago Tribune and Illinois Answers Project set out to investigate the accuracy of property assessments in Cook County, it became clear that reporters would have to use every bit of information at their disposal. This ultimately included public data portals, satellite imagery, mortgage records, deeds, property listings and information extracted from antiquated assessor’s office software.
Like other county and city agencies, the assessor’s office makes data available to the public in an online portal and via mapping technology. Reporters used assessment, mapping and sales data to check out a tip that Cook County Assessor Fritz Kaegi’s office was misclassifying new construction as vacant lots and making other errors while assessing properties across Cook County.
The Tribune’s and Illinois Answers’ analysis included a comparison of property sale prices against the assessor’s first pass fair market values for parcels his office classified as vacant. If a sale of a property classed as vacant was significantly higher than the value set by the assessor, reporters went looking to see if there was actually a building there.
Using public assessment and sales data, reporters limited their search to properties that are or were classified as vacant at the point of sale between 2014 and 2023. Data was filtered to only the most recent sales over $300,000 to capture new homes or developments.
Reporters winnowed the data further to examine properties only where the classification at the point of sale matched the assessed class in 2023 to ensure parcels that were considered vacant when they were sold were also deemed vacant when they were taxed. Reporters also omitted many parcels that were part of multi-parcel sales, meaning they were sold as a group.
Illinois Answers and the Tribune also used tools such as Chicago Cityscape and its Pinmapper tool to confirm and cross-check figures.
As part of an extensive fact-checking process, reporters looked at each parcel on the county’s “CookViewer” GIS system, which has date-stamped satellite imagery over time, with some images going back to 2014. If there was a home or a business on a parcel the assessor considered vacant, or a freshly renovated home that the assessor thought was older or smaller, reporters classified it as “significantly underassessed” and took note of when it looked like it was built.
To be regarded as a “significantly underassessed” property, the building or renovation had to be clearly and substantially complete by April 2023.
Reporters also used this process to identify recently built properties whose assessments were corrected in 2023 after having been left off the rolls for multiple years in order to find examples of homeowners who are facing significant back taxes this year.
Reporters also examined publicly posted Chicago building permit data and filed Freedom of Information Act requests with 22 suburban Cook County municipalities to check recent construction against the assessor’s office’s records to find instances of new construction Kaegi’s office may have missed.
To calculate “missing value,” or the amount in taxable property value that the county was overlooking, reporters subtracted the assessor’s fair market value from the most recent sale price. If a sale was not recorded between 2014 and 2023, that parcel was not included in the missing value calculation.
Building permits are the main triggers signaling for the assessor to revisit the values of certain properties. Permit data going back to 2020 is publicly listed for each property index number (PIN) on the assessor’s website. Reporters logged whether each parcel had public permit data, as well as its status and the type of work that was supposed to be completed.
Older, less detailed permit data is available on the assessor’s office’s previous software system. The assessor provided bulk data from that older system dating back to 2017. If the inspection notes included in that data indicated a property should be rechecked the following year, reporters considered that a trigger for inspection.
Ultimately, Illinois Answers and the Chicago Tribune were able to compile a list of 620 properties that were missing proper assessments for the 2023 tax year alone, adding up to more than $444 million in missed taxable value for the county for that year. The number is conservative and is not exhaustive, since reporters stopped the review of the assessor’s work after it became clear the problem was systemic and occurred across the vast majority of Cook County townships.
