ProPublica Illinois & The Chicago Tribune have created a research-ready dataset of commercial and industrial assessment and appeals data from 2003 to 2016 for the City of Chicago and Cook County, Illinois. The data, which were the underpinning for our analysis in "How the Cook County Assessor Failed Taxpayers," include data on tens of thousands assessments.
Data from the Cook County Assessor's Office and the Illinois Department of Revenue have been cleaned, standardized, and combined to allow for easy analysis of data on various details, including assessed values, sale prices, appeals records, and attorney names. The dataset includes:
- Initial property valuations over multiple reassessment periods within the City of Chicago: The data is compiled by Property Index Number (PIN), a unique identifier that geographically locates each parcel of property. Includes a description of the property class, the assessed value of the property (2008-2015), and a flag to identify properties with identical reassessments over multiple years.
- Data resulting from a sales ratio study comparing the assessor’s valuations to actual sales prices, including comparisons with the first-pass (initial) assessment and the final (board of review) assessment. This analysis used data from the Illinois Department of Revenue (IDOR) real estate transfer declaration data. The data comes from the PTAX declaration form, which provides information on sales of properties throughout the state. The self-reported data includes the classification of the property (such as commercial or residential), the sales price and whether the sale is an arm’s-length transaction or a compulsory sale. The data has been hand-checked to ensure no related parties were included in the analysis, among other exclusions. This entailed examining the buyers and sellers and flagging any who appeared to be related.
- Appeals of commercial and industrial property tax assessments in Cook County. This analysis used appeals data from the CCAO which include data on each PIN that was the subject of an appeal. The data includes initial assessed values (estimates based on market data and building characteristics), second-pass assessed values (which incorporate adjustments based on appeals granted by the assessor’s office) and the final assessed values (incorporating any successful appeals to the Cook County Board of Review). Attorney names are also included in this dataset. The 3.8 million records, which contained many spelling and typographical errors, were standardized using regular expressions and data cleaning tools in R, followed by extensive fact-checking and hand checks.
To request commercial pricing information or purchase the data, complete the form on this page.
Provided in collaboration with Chicago TribuneProPublica & Chicago Tribune