What county is ZIP code 78666 in?
Updated · Data: U.S. Census Bureau
ZIP code 78666 (San Marcos, TX) is mostly in Hays County (77.9% of its land), with parts in Guadalupe County and Comal County and Caldwell County.
Which counties is ZIP 78666 in?
| County | Share of land area | Chart |
|---|---|---|
| Hays County | 77.9% | |
| Guadalupe County | 15.7% | |
| Comal County | 4.3% | |
| Caldwell County | 2.0% |
About 87,775 people live in this ZIP code area. Because it crosses a county line, the county depends on the street: check your address.
Is ZIP 78666 a Census ZIP code area?
Yes. A ZIP Code Tabulation Area (ZCTA) is the Census version of a ZIP code; its edges can differ from USPS delivery routes (ZIP code vs ZCTA). Look up another ZIP on the ZIP code to county lookup.
Sources: Census 2020 ZCTA-county relationship file; Gazetteer 2024; GeoNames (CC BY 4.0, post office name); ACS 2019-2023 5-year. Data as of November 1, 2026. Not affiliated with USPS or any government agency.
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