ZIP 78666 falls in Hays County, Texas, where we hold 56,993 parcels measured as septic county-wide and 32,829 on sewer. We do not have a per-ZIP parcel count for this county, so this is the county total, not a count specific to ZIP 78666.
ZCTA 78666 is not entirely inside one county. Land-area share is from the 2020 Census ZCTA-to-county relationship file.
| County | Land in this ZIP | Documents held | On septic (county) | On sewer (county) |
|---|---|---|---|---|
| Hays County, Texas | 78% | 2 | 56,993 | 32,829 |
| Guadalupe County, Texas | 16% | 11 | 36,043 | 31,861 |
| Comal County, Texas | 4% | 99,906 | 53,050 | 16,927 |
| Caldwell County, Texas | 2% | 8 | — | — |
Land-area overlap is from the 2020 Census Bureau ZCTA5-to-county relationship file, not an estimate of ours. Parcel and document counts are rows we hold, not a survey of every property in the ZIP. Last verified 2026-09-01.
We hold 56,993 parcels measured as septic for Hays County, Texas as a whole, not broken out by ZIP.
ZIP 78666 spans 4 counties: Hays County, Texas, Guadalupe County, Texas, Comal County, Texas, Caldwell County, Texas.