Zillow Transaction and Assessment Database (ZTRAX), United States, 1940-2020

Note data is restricted and requires an application process and IRB approval.

The Zillow Transaction and Assessment Dataset (ZTRAX) is the country's largest real estate database. Zillow makes the data available in the interest of greater transparency in the real estate market.

ZTRAX's temporal coverage varies greatly by county. Some counties have digitized records extending back to the early 1990s, whereas other counties have only provided data to the mid-2000s. In Zillow's work analyzing these data to create home value indices, they have found sample sizes are sufficient for most areas going back to April 1996.

Zillow sources ZTRAX from a major large third-party provider and supplemented through an internal Zillow initiative called "County Direct." The data coverage gaps inherited through the third-party source are due to county recording procedures, as well as the data collection process of that third party. Changes to the collection process have occurred over time due to mergers and other organizational changes, as well as process improvements. Because of the gaps in coverage, Zillow instituted its County Direct program. This program prioritizes counties on a variety of characteristics and supplements the third-party coverage by collecting data directly from county assessor and recorder's offices.

These data include:

• More than 400 million detailed public records across 2,750+ U.S. counties;
• More than 20 years of deed transfers, mortgages, foreclosures, auctions, property tax delinquencies, and more, for both commercial and residential properties;
• Property characteristics, geographic information, and prior valuations for approximately 150 million parcels in 3,100+ counties nationwide.

ZTRAX does not contain:

• Zestimates
• Rent data (such as rent prices)
• Listing data (such as time on market)
• User search data

The ZTrax data will be updated approximately twice per year.

These datasets are very large. Researchers wishing to use the data should plan to download subsets containing only the geographic areas in which they are specifically interested. ICPSR suggests going to the following resources for code on utilizing the ZTrax data:

• GitHub - zillow-research/ztrax: A repository for dataset creation code using ZTRAX.
• Import ZTRAX Flat Files to R or SQL Database * ztraxr
• https://github.com/matthewstern/ztrax
• https://placeslab.org/hedonic-data-practices/.
• Additional text resources for guidance in using the data can be found in the Data-related Publications for this study.

These data are now solely distributed through ICPSR. Users can begin the process of applying to access the data using the button on the study homepage.