A brief outline of the changes users can expect from the Assessor's open data offerings.

The bid tabulations provided herein are preliminary and are for informational purposes only. The purpose of providing this preliminary information is to improve process transparency. The information contained in the preliminary bid tabulations is subject to change pending math review, analysis of all bids, and review of documentation provided.
Bids: All bids estimated at $25,000 or more are publicly opened and read at the time, date, and place specified in the bid document.
RFP/RFQ/RFI: Responses to RFP/RFQ/RFI are not publicly opened. Names of respondents will be made available based on the names identified on the sealed package and is, therefore, subject to change.

For bid tabulations before June 2016 see https://datacatalog.cookcountyil.gov/d/pn38-yupm

2012 budget requests by line-item, by bureau, and elected official.

This dataset provides a cumulative record of payment and invoice details for County suppliers, vendors and other payees. Data is from December 1, 2016 to present. Payment data prior to December 1, 2016 is archived in the Cook County Check Register here: https://datacatalog.cookcountyil.gov/Finance-Administration/Cook-County-Check-Register/gywr-fjeh

The Parcel 2015 feature contains tax parcel polygons for the 2015 property tax assessment at the County. This feature reflects tax parcel polygons as they existed from 1/1/2015 through 12/31/2015. Each parcel is uniquely identified with a Property Index Number (PIN).

This data set contains characteristic data points used by the Cook County Assessor in the 2021 Chicago reassessment to produce initial estimates of the current market value of most Chicago homes (single-family homes, small multi-family homes, and condo units). You can use the "Filter" option to search for a property's PIN or address, and see what data the Assessor’s Office had about a home’s characteristics at the time of modeling*. To learn more about how the 2021 model used this data, read about our public Residential Automated Valuation Model here. Chicago properties not listed here are reassessed using different modeling procedures.

*Important Note: This dataset is, at the time of publication, an early snapshot of data. Data about a home might change later in the assessment process this year as Assessor’s Office staff and analysts review these properties. After this review, updated characteristics and market values are mailed to homeowners. If the data listed on the assessment notice is incorrect, an appeal can be filed to provide the correct characteristics.

As of February 14, 2020 this dataset will be considered archived information and will no longer be updated.

First-pass property values as assessed by the Cook County Assessor in their Computer Assisted Mass Appraisal system used to assess residential properties. This dataset contains first pass values for 2019 and corresponds with residential PINs in the Cook County Assessor's Assessment Data. These are NOT final assessed values. For Disclaimers, see dataset narrative at https://datacatalog.cookcountyil.gov/stories/s/p2kt-hk36

Metropolitan Water Reclamation Taxing Districts in Cook County

Commercial valuation data collected and maintained by the Cook County Assessor's Office, from 2021 to present. The office uses this data primarily for valuation and reporting. This dataset consolidates the individual Excel workbooks available on the Assessor's website into a single shared format. Properties are valued using similar valuation methods within each model group, per township, per year (in the year the township is reassessed). This dataset has been cleaned minimally, only enough to fit the source Excel workbooks together - because models are updated for each township in the year it is reassessed, users should expect inconsistencies within columns across time and townships.

When working with Parcel Index Numbers (PINs) make sure to zero-pad them to 14 digits. Some datasets may lose leading zeros for PINs when downloaded.

This data is property-level. Each 14-digit key PIN represents one commercial property. Commercial properties can and often do encompass multiple PINs. Additional notes:

• Current property class codes, their levels of assessment, and descriptions can be found on the Assessor's website. Note that class codes details can change across time.


• Data will be updated yearly, once the Assessor has finished mailing first pass values. If users need more up-to-date information they can access it through the Assessor's website.


• The Assessor's Office reassesses roughly one third of the county (a triad) each year. For commercial valuations, this means each year of data only contain the triad that was reassessed that year. Which triads and their constituent townships have been reassessed recently as well the year of their reassessment can be found in the Assessor's assessment calendar.


• One KeyPIN is one Commercial Entity.


• Each KeyPIN (entity) can be comprised of one single PIN (parcel), or multiple PINs as designated in the pins column.


• Additionally, each KeyPIN might have multiple rows if it is associated with different class codes or model groups. This can occur because many of Cook County's parcels have multiple class codes associated with them if they have multiple uses (such as residential and commercial).


• Commercial properties are calculated by first determining a property’s use (office, retail, apartments, industrial, etc.), then the property is grouped with similar or like-kind property types. Next, income generated by the property such as rent or incidental income streams like parking or advertising signage is examined. Next, market-level vacancy based on location and property type is examined. In addition, new construction that has not yet been leased is also considered. Finally, expenses such as property taxes, insurance, repair and maintenance costs, property management fees, and service expenditures for professional services are examined. Once a snapshot of a property’s income statement is captured based on market data, a standard valuation metric called a “capitalization rate” to convert income to value is applied.


• This data was used to produce initial valuations mailed to property owners. It does not incorporate any subsequent changes to a property’s class, characteristics, valuation, or assessed value from appeals.

Township codes can be found in the legend of this map.

For more information on the sourcing of attached data and the preparation of this dataset, see the As