Cook County Assessor’s Office Releases Permits Dataset


Cook County Assessor’s Office Releases Permits Dataset 

The Cook County Assessor’s Office released a new public dataset containing building permits submitted to the office by municipalities. 

 The data can be found here on Cook County’s Open Data Portal. 

This release creates access to the data for all permits stored in iasWorld, the office’s system of record. Publishing the data allows users to search (for example, for a specific municipality), filter, sort, and download the data. More than half a million rows of permit data are included in the dataset.  

 “In line with our longstanding commitment to transparency in assessments, my office regularly releases new data to the public. This release continues that commitment.” said Cook County Assessor Fritz Kaegi. “I hope researchers, reporters, and Cook County residents can explore this information to learn more about how our property tax system works.”   

Permits list new construction and changes to a property that can change its assessed value and grow the tax base. The CCAO receives permits from municipalities and sorts them, determining whether the kind of work done on the property is likely to result in a new assessed value. If it is, a field inspection may take place.  

 Permits are also used to administer the Home Improvement Exemption. When homeowners add an improvement to their home, they aren’t taxed on up to $75,000 of the added value for up to four years. The CCAO automatically applies this exemption after receiving a building permit and conducting a field check on the property.   

Over the last six years, the CCAO has hired more staff, implemented new technology, and improved our processes to better capture accurate data from permits.   

In addition to the release of this dataset, our office has made several other recent changes to eliminate bottlenecks and improve accuracy in our permit processing. 

• Conducted an audit of 27,000 permits. In the fourth quarter of 2024, we conducted an audit of 27,000 permits in our system. We found that around a third of these permits needed a second look. These will be processed and field inspected over the course of 2025 to bring any missing value onto the tax rolls.  

• Began processing permits for 2025 early. Permit processes have been streamlined, allowing our office to begin work on 2025 permits at the end of 2024. With this head start on permit processing, our field inspectors will have to conduct fewer field inspections when townships open for reassessment, ensuring that our work is more accurate and efficient.  

  • Continue to utilize technologies that catch property changes. Since 2020, our office has contracted with Pushpin, a company that develops change detection technology. This kind of technology takes images of land from satellites and drones and determines whether there’s been a change. For us, it’s a useful safeguard. If we don’t receive permit data for a property from a municipality, these images can help us determine whether there’s been new construction and let us know if we should send a field inspector to the site. In 2025, we will continue using Pushpin to flag possible properties for inspection. 

• Continue to increase staffing levels in our Data Integrity department. In the last year, we have hired a dozen new employees in the Data Integrity department, which is responsible for taking in and processing permits. This includes 7 residential field inspectors, 2 permit specialists, and 3 industrial/commercial field inspectors, bringing our total number of Data Integrity employees to 37. For FY2025, we were given the budget for an additional 3 industrial/commercial field inspectors, whom we plan to hire over the course of the year. By increasing our staffing levels, we are ensuring that permits will be processed and inspected for changes in a timely manner.


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