Land, building, and total assessed values, pre and post-appeal with the Cook County Assessor’s office, for all Cook County parcels, from 1999 to present. The Assessor's Office uses these values for reporting, evaluating assessment performance over time, and research.

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

This data is parcel-level. Each row contains the assessed values for a single PIN for a single year pre and post-appeal. Important notes:

• This dataset includes appeal cases that are currently open. Data for these cases is not final and is subject to change.


• Each row includes two stages: 1) mailed, these are the initial assessed values (AVs) estimated by the Assessor's Office and mailed to taxpayers. The columns mailed_bldg, mailed_land, and mailed_tot are the AVs for the building, land, and total, at the mailed stage. 2) certified, these are values after the Assessor's Office closes appeals. The columns certified_bldg, certified_land, and certified_tot are the AVs for the building, land, and total, after the Assessor has completed appeal decisions.


• Values in this dataset are not final assessed values for a given year as they are still subject to change if a taxpayer appeals to the Cook County Board of Review. At present, this dataset does not contain appeal decisions from this final third stage. However, the final stage AVs and appeal decisions can be downloaded from the Board of Review Appeal Decision History dataset.


• Due to the current transition from the county's legacy system to a modern system of record, appeal data is sparse prior to 2021. Values and change/no change decisions are available, but the reason, agent, and type fields will only be complete once the new system has been successfully batch updated with complete historical data.


• The values in this data are assessed values, NOT market values. Assessed values must be adjusted by their level of assessment to arrive at market value. Note that levels of assessment have changed throughout the time period covered by this data set.


• This data set will be updated monthly regardless of the Assessor's mailing and certification schedule. There may be small discrepancies between the Assessor's site and this data set, as each pulls from a slightly different system. If you find a discrepancy, please email the Data Department using the contact link below.


• This dataset contains data for the current tax year, which may not yet be complete or final. Assessed values for any given year are subject to change until review and certification of values by the Cook County Board of Review, though there are a few rare circumstances where values may change for the current or past years after that.


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


• 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 preparation of this dataset, see the Assessor's Standard Operating Procedures for Open Data on GitHub.

The railroad feature data layer depicts the location of railroad tracks (including single and multiple line tracks, railyards, and spurs) and railroad stations in Cook County, Illinois.

By ordinance, the investigations and considerations by the Board of Ethics of potential violations of the Ethics Ordinance are confidential. County Code, § 2-592. As a matter of policy, the Board also maintains as confidential the identity of the requestors of advisory opinions. Board of Ethics Rules & Regulations, § 4.10. The Board, however, is undertaking to make its final determinations available to the public with such deletions as may be necessary to prevent disclosure of any information the Board determines to be confidential.

The Public Land Survey System (PLSS) forms the foundation of Cook County's cadastral system for identifying and locating land records. Tax parcels are identified using township and section notation, in a modified format. This PLSS feature data set is intended to correspond to tax pages in the Cook County Assessor's Tax Map book (current as of tax year 2000 for 66% of the County and as of tax year 2001 for the remaining 33% of the County), and should not be used for measurement or surveyor purposes. In addition, the parcel attributes PINA (area/township) and PINSA (subarea/section) do not necessarily correspond to the PLSS township and section polygon in which a given parcel resides. The PLSS data is modeled as a single composite network coverage that encompasses townships (area), sections (subarea), quarter sections, and half quarter section.

Updated periodically--Click on the link to see or download a .pdf of material related to the contract.

Real estate sales data used by the Cook County Assessor to estimate Fair Cash Values for the purpose of property taxation. Deeds that include multiple PIN numbers are excluded from this data. This data is produced by joining sales data from the Illinois Department of Revenue against incomplete sales data from the Cook County Recorder of Deeds, parsing the resulting data to obtain data unique by deed number, and, in some cases, determining arms' length status of sales.

Paved road edge polygons show the location of pavement edges along a road