Assessor - Single and Multi-Family Improvement Characteristics

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 monthly. 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.

Read about the Assessor's 2025 Open Data Refresh.

Data and Resources

Field Value
accessLevel public
catalog_@context https://project-open-data.cio.gov/v1.1/schema/catalog.jsonld
catalog_@id https://datacatalog.cookcountyil.gov/data.json
catalog_conformsTo https://project-open-data.cio.gov/v1.1/schema
catalog_describedBy https://project-open-data.cio.gov/v1.1/schema/catalog.json
identifier https://datacatalog.cookcountyil.gov/api/views/x54s-btds
issued 2025-02-14
landingPage https://datacatalog.cookcountyil.gov/d/x54s-btds
modified 2025-09-01
publisher datacatalog.cookcountyil.gov
resource-type Dataset
source_datajson_identifier true
source_hash e04ff71e1c269d92c1fa5703be6609d92018156f820b3ea23a87cbd24b6dcc17
source_schema_version 1.1
theme {"Property & Taxation"}
Groups
  • AmeriGEOSS
  • National Provider
  • North America
Tags
  • AmeriGEO
  • AmeriGEOSS
  • CKAN
  • GEO
  • GEOSS
  • National
  • North America
  • United States
  • cook-county-assessor
  • property-tax
isopen False
license_id notspecified
license_title License not specified
maintainer Cook County Assessor's Office Data Department
maintainer_email no-reply@datacatalog.cookcountyil.gov
metadata_created 2025-09-23T19:11:52.774663
metadata_modified 2025-09-23T19:11:52.774667
notes 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 <a href="https://prodassets.cookcountyassessor.com/s3fs-public/form_documents/classcode.pdf">on the Assessor's website</a>. 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 monthly. Rowcount and characteristics for the current year are only final once the Assessor <a href="https://www.cookcountyassessor.com/assessment-calendar-and-deadlines">has certified the assessment roll</a> 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 <a href="https://github.com/ccao-data/wiki/blob/master/Residential/Home-Improvement-Exemptions.md">Assessor's Data Department wiki</a>. For more information on how this data is used to estimate property values, see the <a href="hhttps://github.com/ccao-data/model-res-avm">Assessor's residential modeling code</a> on GitHub. Township codes can be found <a href="https://prodassets.cookcountyassessor.com/s3fs-public/page_comm/trimap.pdf">in the legend of this map</a>. For more information on the sourcing of attached data and the preparation of this dataset, see the <a href="https://github.com/ccao-data/wiki/blob/master/SOPs/Open-Data.md">Assessor's Standard Operating Procedures for Open Data</a> on GitHub. <a href="https://datacatalog.cookcountyil.gov/stories/s/gzdr-q7c4">Read about the Assessor's 2025 Open Data Refresh.</a>
num_resources 4
num_tags 10
title Assessor - Single and Multi-Family Improvement Characteristics