Cook County Property Assessment Appeal Decisions Since 2010

Cook County, Illinois parcel-level data contains historic land, building, and total assessed values for properties appealed with the Board of Review from 2010 onward. The County of Cook prepares this data for internal purposes and provides it publicly as a courtesy. Each row represents a single Parcel Index Number (PIN) for a single year, showing values certified after appeal closure.

Use Cases

• Analyze trends in Assessor_LandValue and Assessor_ImprovementValue versus BOR-adjusted values (BOR_LandValue, BOR_ImprovementValue) to measure appeal outcomes.
• Model AppealType (e.g., residential, commercial) or MajorClass as a function of Appellant_Zip, Appellant_Address, and AttorneyCode to identify appeal patterns.
• Cluster parcels by lat and long coordinates to perform geospatial analysis of appeal density and assessment changes across townships.
• Predict ChangeReasonDescription or NoChangeReasonDescription using features like AppealTrk, PIN10, and township_code for appeals from 2015 onward.
• Track annual assessment volatility by joining on PIN_dash or pin across years to compare Assessor_TotalValue over time.

Strengths

• Time series spans from 2010 to present, offering over a decade of appeal history.
• Includes geospatial coordinates (lat, long, centroid_geom) for parcel-level mapping.
• Contains multiple value columns (Assessor and BOR) for before/after appeal comparison.

Limitations

• Assessed values are not market values and require adjustment by level of assessment, which has changed over time.
• ChangeReason and NoChangeReason fields are only populated starting in 2015, limiting earlier year analysis.
• Discrepancies may exist between this dataset, the Board of Review's data, and the Assessor's site as they pull from different systems.

Provenance

Source

County of Cook Board of Review, via datacatalog.cookcountyil.gov.

Collection Method

Collected for internal reporting and research purposes during the appeal certification process.

Time Range

2010 to present.

Freshness

Updated when each township is certified; last metadata update was 2026-01-27.

Geography

Cook County, Illinois, United States.