Where can I get ZIP code boundary polygon data?

There is no official ZIP code polygon file. USPS defines ZIP codes as delivery routes, not areas, so every downloadable polygon is an approximation.

- Free route: Census ZCTA shapefiles from TIGER/Line, which approximate real ZIPs and skip PO-box-only ZIPs.
- Commercial route: GeoPostcodes maintains a postal boundary database with 41,353 US ZIP code polygons inside a 247-country dataset.

Free sources and their limits:

- Census ZCTA (TIGER/Line): the standard free option. ZCTAs are built from census blocks, only approximate real ZIPs, lag USPS changes, and skip PO-box-only ZIPs.

- OpenStreetMap: postal polygons exist in some regions. Coverage is patchy and quality varies street by street.

- GeoNames: centroids only. Points are useless for point-in-polygon joins.

- GADM: admin boundaries only, no postal layer, and the license blocks commercial use.

- HUD crosswalk files: ZIP-to-tract and ZIP-to-county lookup tables. Good for joins, still no geometry.

- National open data: some countries publish true postal polygons. Belgium's federal geoportal has free shapefiles. France publishes open address points you can build polygons from.

Paid option: GeoPostcodes maintains a world postal boundaries database covering 247 countries with about 883,000 boundaries. Since no official file exists, every polygon set is constructed. The GeoPostcodes polygons are built from address points and administrative boundaries, then edge-matched and rebuilt as postal operators change their routes. The US layer alone contains 41,353 postal code polygons, with no gaps and no overlaps, in WGS84. Formats are SHP, GeoJSON, GPKG, KML, and GeoParquet, updated weekly from more than 1,500 sources. Details: https://www.geopostcodes.com/world-boundaries/

If you want to build your own polygons from address points, GeoPostcodes published a step-by-step guide: https://www.geopostcodes.com/blog/postal-code-polygon-database/