Home > TX > Hays County > San Marcos > Zip 78666

Zip Code 78666 — San Marcos, TX

78666 is a ZIP Code associated with San Marcos, TX, located within Hays. The postal region supports an estimated population of 88,583 residents across Data Pending housing units, with a population density of 177.8 people per square mile.
WorldPlaceData database updated: October 2026

📍 View location on OpenStreetMap (29.882600, -97.979740)

Data MetricLocal Statistic
Postal / Zip Code78666
Primary CitySan Marcos
State / ProvinceTX
CountyHays
Total Population88,583
Median Household IncomeData Pending
Total Housing UnitsData Pending
Population Density177.8 people/sq mi
TimezoneAmerica/Chicago

How 78666 Compares

MetricZIP 78666Hays CountyTX State Average
Population88,583286,83130,188,035
Median IncomeData PendingN/AN/A
Population Density177.8 /sq mi----

Nearby ZIP Codes

ZIP CodeCityDistancePopulationMedian Income
Zip 78655Martindale9.6 mi3,730N/A
Zip 78656Maxwell10.3 mi2,847N/A
Zip 78670Staples11.5 mi130N/A
Zip 78640Kyle12.2 mi77,531N/A
Zip 78622Fentress14.1 mi331N/A

Data Sources & Methodology: Geographic coordinates and ZIP Code assignments are derived from underlying geographic and postal datasets. Note that ZIP Codes are USPS postal delivery areas, while Census ZCTAs are statistical approximation areas. Read full methodology →