ZIP 78664 falls in Williamson County, Texas, where we hold 110,116 parcels measured as septic county-wide and 176,652 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 78664.
ZCTA 78664 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) |
|---|---|---|---|---|
| Williamson County, Texas | 86% | — | 110,116 | 176,652 |
| Travis County, Texas | 14% | 164,420 | 34,543 | 337,990 |
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 110,116 parcels measured as septic for Williamson County, Texas as a whole, not broken out by ZIP.
ZIP 78664 spans 2 counties: Williamson County, Texas, Travis County, Texas.