Data attribution

County and state outlines are the 1:10,000,000 cartographic boundaries from the US Census Bureau, redistributed inus-atlas(public domain). The file served here is counties-10m.json.

Time zone polygons come fromtimezone-boundary-builderby Evan Siroky and contributors. That database © OpenStreetMap contributors and is licensed under theOpen Database License. Lookups use geo-tz 8.1.11 and its “alike since 1970” extract. Release 2026f of timezone-boundary-builder was current on 1 November 2026.

The county index produced by this site (/geo/county-index.json) is a derived work of that database. It is made available under the same ODbL terms. Attribute timezone-boundary-builder and OpenStreetMap if you reuse it.

Legal descriptions are quoted and paraphrased from49 CFR Part 71, which is a work of the US government. Indiana's 12 Central counties also match the list on IN.gov.

Unresolved sample issues are listed in DATA_TODO.md in the source repository.