Cook County Condominium Unit Characteristics With Ownership Proration

Unit-level data for residential condominiums in Cook County, collected by the Assessor's Office from 1999 to present. The dataset includes characteristics like unit square footage, number of bedrooms, and bathrooms, but these detailed features are only available on a per-triad basis after 2021. It is used primarily for property valuation, assessments, and reporting.

Use Cases

• Analyzing condominium unit valuation trends over time using `tax_year`, `unit_sf`, `num_bedrooms`, and `class`.
• Modeling ownership percentages within a building by aggregating `pin_proration_rate` and `card_proration_rate` for units sharing a `pin10`.
• Identifying non-residential condominium parcels like parking or storage units using the `is_parking_space` and `is_common_area` flags.
• Studying building-level characteristics by grouping unit records (`pin`) by their building identifier (`pin10`) and examining `building_sqft` and `year_built`.

Strengths

• Provides a long-term time series with data from 1999 to present, enabling longitudinal analysis.
• Includes detailed unit-level attributes such as `unit_sf`, `num_bedrooms`, `num_full_baths`, and `num_half_baths` for records after 2021.
• Contains specific fields for proration analysis (`pin_proration_rate`, `card_proration_rate`) and non-residential unit identification (`is_parking_space`).

Limitations

• Detailed unit characteristics (square footage, bedrooms) are only consistently available on a per-triad basis after 2021, limiting historical analysis.
• Platforms disagree on the last update date, with one listing 2026-04-05 and another 2026-04-01.
• Row counts, dataset size, license, and author information are not provided by any source.

Provenance

Source

Cook County Assessor's Office

Collection Method

Manually compiled from a variety of sources since 2021, with ongoing efforts to clean and identify unit records.

Time Range

1999 to present

Freshness

Updated monthly, with the most recent platform update noted as 2026-04-05.

Geography

Cook County, Illinois, USA