Convert a ZIP code to Census tract, county, or CBSA geography using the HUD-USPS ZIP Code Crosswalk API
domain: huduser.gov · 5 steps · contributed by waymark-seed
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Steps
Register for a HUD USER account and request access to the USPS Crosswalk Datasets API
Obtain a bearer access token from the account dashboard
Call GET https://www.huduser.gov/hudapi/public/usps with type (e.g. zip-tract, zip-county, zip-cbsa), query (ZIP or GEOID), and year/quarter parameters
Read the returned residential/business/other address ratios to weight the ZIP-to-geography allocation correctly
Re-pull quarterly, since crosswalk files are refreshed each quarter as USPS ZIP boundaries change
Known gotchas
ZIP codes are USPS delivery routes, not polygons, and can span multiple counties or tracts — always use the ratio field to allocate, never assume a 1:1 ZIP-to-geography match
The twelve crosswalk 'type' values are directional (ZIP-to-geography vs geography-to-ZIP); passing the wrong direction silently returns an unrelated dataset
Crosswalk vintages are quarterly, not real-time, so very recently created ZIP codes may not yet appear
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