ZTRAX: Zillow Transaction and Assessment Dataset (licensed)
ZTRAX (the Zillow Transaction and Assessment Dataset) was a national, property-level database covering hundreds of millions of records nationwide: deed transfers (sales, prices, mortgages, foreclosures) and assessor / tax-roll data (property characteristics, assessed values, owner information) across U.S. counties. It was the standard research source for parcel-level housing transactions before Zillow ended the academic program. A paper we distill uses it: Slutzky & Xu use ZTRAX real-estate transactions (1993 to 2020; about 9 million Maryland transactions, with foreclosure events identifiable post-2007) for foreclosure events and the property-matched sample behind the foreclosure and combined insolvency tests when estimating the effect of pretrial detention on household financial distress.
- Cost: was free to academic and nonprofit researchers under a signed Zillow data-use agreement; not an open public download. The program was discontinued in 2023, so new access is no longer granted.
- Vendor: Zillow (ZTRAX). Coverage and successor products differ; some researchers now turn to commercial deed/assessor vendors instead.
- Coverage: parcel-level deeds and assessor records for most U.S. counties, back to the early 1990s where county records allow; transaction history depth varies by county.
Access (when licensed)
Section titled “Access (when licensed)”- Was through a Zillow data-use agreement. Approved researchers downloaded the full transaction and assessment files (large fixed-width tables with a layout document) and matched on property identifiers. New agreements are no longer issued.
- Two linked grains. A transaction table (deed events: sale, mortgage, foreclosure, dates, amounts) and an assessment table (property characteristics, assessed value, owner), joined on a Zillow property identifier (RowID / ImportParcelID).
- Where a researcher still holds a legacy copy under their prior agreement, keep
any credentials or keys in
.env, never hard-coded, and respect the agreement’s redistribution limits.
Gotchas (the ones that bite pipelines)
Section titled “Gotchas (the ones that bite pipelines)”These are the failure modes to expect; they are documented, not verified here.
- The program is discontinued. ZTRAX is no longer obtainable from Zillow; results built on it are not reproducible by a new user without a legacy copy. A pipeline cannot acquire it today. Plan for a commercial deed/assessor vendor if you need fresh access.
- County coverage and history depth are uneven. Transaction back-history, field completeness, and whether prices are recorded depend on each county’s recording practice; absence of a record is often missing data, not absence of a sale. The citing paper’s coverage scopes to Maryland for this reason.
- Deed records mix arms-length and non-arms-length transfers. Quitclaims, intra-family transfers, refinancings, and foreclosure deeds all appear; filtering to genuine market sales (by document type and price) is required before treating a transfer as a sale. Foreclosure identification is reliable only from the post-2007 deeds in the citing paper.
- Matching to people or addresses is fuzzy. Owner names and addresses need standardization; linking ZTRAX parcels to individuals (as the citing paper does to court records) is a probabilistic match that drops and mismatches observations. Document the match rate.
- Large, layout-heavy files. The raw tables are big fixed-width extracts with a separate layout document and shifting schemas across vintages; a loader built for one delivery can silently misparse another. Validate against the layout file.
Citation
Section titled “Citation”Cite the source and product, e.g.: Zillow Transaction and Assessment Dataset (ZTRAX), Zillow, [dates], accessed YYYY-MM-DD (academic data-use agreement; program discontinued 2023). State the counties and date range, the transaction filters applied, and the match procedure used to link parcels to other records.