2021 assessor neighborhoods used by the Cook County Assessor's Office for valuation and reporting.

Neighborhood polygons used by the Cook County Assessor's Office for valuation and reporting. These neighborhoods are specific to the Assessor. They are intended to represent homogenous housing submarkets, NOT Chicago community areas or municipalities.

These neighborhoods were reconstructed from individual parcels using spatial buffering and simplification. The full transformation script can be found on the Assessor's GitHub.

Residential condominium unit characteristics collected and maintained by the Assessor's office for all of Cook County, from 1999 to present. The office uses this data primarily for valuation, assessments, and reporting.

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 unit-level. Each 14-digit PIN represents one condominium unit. The first 10 digits of each PIN are the condominium building. Additional notes:

• The Assessor's Office has historically not tracked any internal, unit-level characteristics for condominiums, including square footage, number of bedrooms, etc. In 2021, the office began to manually compile unit-level data from a variety of sources. The ultimate intention is to gather basic data on all condominium units in the county.


• As such, unit square footage, building total square footage, and unit number of bedrooms are only available on a per-triad basis after 2021. Future data updates will add these features for other areas.


• Condominiums are assessed based on their percentage of ownership. See the link below for more information on how this process works. The percentage of ownership for all units in a building should sum to 1. However, this may not always be the case in this data, since it does not include commercial units.


• Condominium parcels can also be parking areas, storage units, or common areas. Identifying these units can be challenging, and they are not valued using mass appraisal. The Assessor's Office has an ongoing effort to clean up and identify these unit records.


• 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 bi-weekly.


• Depending on the time of year, some third-party and internal data will be missing for the most recent year. Assessments mailed this year represent values from last year, so this isn't an issue. By the time the Data Department models values for this year, those data will have populated.


• Rowcount and characteristics for the current year are only final once the Assessor has certified the assessment roll for all townships.

For more information on how this data is used to estimate condominium unit values, see the Assessor's condominium modeling code on GitHub.

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 Assessor's Standard Operating Procedures for Open Data on GitHub.

This dataset contains address points for addresses in Cook County. An ESRI Service is available at: https://hub-cookcountyil.opendata.arcgis.com/datasets/5ec856ded93e4f85b3f6e1bc027a2472_0/

Data is updated and maintained by Cook County GIS.

Suburban Cook County Election Precincts maintained by the Cook County Clerk's Election Department. Not included are the City of Chicago Election Precincts which are maintained by the Chicago Board Of Elections. An ArcGIS Service is available at: https://hub-cookcountyil.opendata.arcgis.com/datasets/0e91b48d49744346be343f0cb99d25bd_0/

Voting District Project of the Census Redistricting Data Program commenced in Summer of 2017 to establish the state’s Voting precincts within the bureau’s tiger geography. The initial phase used the Bureau’s GUPS plugin for QGIS to update the districts from the 2010 round, and then a secondary verification phase took place to ensure the updated voting districts were properly enacted into Tiger geographic files. A post census effort took place in December 2021 to cut the number of precincts down countywide to 1430.
Election Data Services conducted Phase 2 of the Census Redistricting Data Program for the State of Illinois, as well as implemented changes made post census in Cook County.

Precincts are updated as needed before every election by the Cook County Clerk's Elections Department.

Single and multi-family (less than 7 units) property characteristics collected and maintained by the Assessor's Office for all of Cook County, from 1999 to present. The office uses this data primarily for valuation and reporting.

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.

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.

This data is improvement-level - 'improvements' are individual buildings on a parcel. Each row in a given year corresponds to a building e.g. two rows for the same parcel in one year means a parcel has more than one building.

Data will be updated bi-weekly. Rowcount and characteristics for the current year are only final once the Assessor has certified the assessment roll for all townships.

Depending on the time of year, some third-party and internal data will be missing for the most recent year. Assessments mailed this year represent values from last year, so this isn't an issue. By the time the Data Department models values for this year, those data will have populated.

NOTE: The Assessor's Office has recently changed the way Home Improvement Exemptions (HIEs) are tracked in its data. HIEs "freeze" a property's characteristics for a period of time with the intention of encouraging owners to improve their property without fear of assessment increases.

Historically, the updated, "improved" characteristics were saved in a separate file. However, in more recent years, the improved characteristics are saved in the main characteristics file. As such, the records in this data set from before 2021 do NOT include HIE characteristic updates, while those after and including 2021 DO include those updates.

For more information on HIEs, see the Assessor's Data Department wiki.

For more information on how this data is used to estimate property values, see the Assessor's residential modeling code on GitHub.

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 Assessor's Standard Operating Procedures for Open Data on GitHub.

A complete, historic universe of Cook County parcels with attached geographic, governmental, and spatial data.

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.

Additional notes:

• Data is attached via spatial join (st_contains) to each parcel's centroid.


• Centroids are based on Cook County parcel shapefiles.


• Older properties may be missing coordinates and thus also missing attached spatial data (usually they are missing a parcel boundary in the shapefile).


• Newer properties may be missing a mailing or property address, as they need to be assigned one by the postal service.


• Attached spatial data does NOT go all the way back to 1999. It is only available for more recent years, primarily those after 2012.


• The universe contains data for the current tax year, which may not be complete or final. PINs can still be added and removed to the universe up until the Board of Review closes appeals.


• Data will be updated monthly.


• Rowcount and characteristics for a given year are final once the Assessor has certified the assessment roll for all townships.


• Depending on the time of year, some third-party and internal data will be missing for the most recent year. Assessments mailed this year represent values from last year, so this isn't an issue. By the time the Data Department models values for this year, those data will have populated.


• 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.


• Due to decrepencies between the systems used by the Assessor and Clerk's offices, tax_district_code is not currently up-to-date in this table.

For more information on the sourcing of attached data and the preparation of this dataset, see the Assessor's data architecture repo on GitLab.

Update 10/31/2023: Sales are no longer filtered out of this data set based on deed type, sale price, or recency of sale for a given PIN with the same price. If users wish to recreate the former filtering schema they should set sale_filter_same_sale_within_365, sale_filter_less_than_10k, and sale_filter_deed_type to False.

Parcel sales for real property in Cook County, from 1999 to present. The Assessor's Office uses this data in its modeling to estimate the fair market value of unsold properties.

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.

Sale document numbers correspond to those of the Cook County Clerk, and can be used on the Clerk's website to find more information about each sale.

NOTE: These sales are filtered, but likely include non-arms-length transactions - sales less than $10,000 along with quit claims, executor deeds, beneficial interests are excluded. While the Data Department will upload what it has access to monthly, sales are reported on a lag, with many records not populating until months after their official recording date.

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.

For more information on the sourcing of attached data and the preparation of this dataset, see the Assessor's Standard Operating Procedures for Open Data on GitHub.