St. Louis County GIS — St. Louis County, Missouri open geospatial data (ArcGIS). Enables searching and querying datasets like parcels, addresses, zoning and public works.
Owner, APN and address lookup across 479 US counties (494 verified ArcGIS REST endpoints, all 50 states plus DC), plus city code-violation, building-permit and zoning-case datasets. No API key; built on public county GIS data.