78666 ZIP Code: San Marcos, Texas
Official postal information, geographic coordinates, USPS post office locations, and US Census Bureau demographic metrics for postal code 78666 in San Marcos, TX.
Postal & Geographic Specifications USPS Data
Demographic & Economic Profile (US Census Bureau)
American Community Survey (ACS) 5-Year Verified Metrics
Editor's Neighborhood Insight & Local Context
78666 is an active postal delivery zone serving San Marcos in Hays County, Texas. Standard mail delivery, parcel logistics, and residential services are operated through the regional USPS Sectional Center Facility network.
Designated USPS Post Office Facility Mail & Parcel Drop-off
Mon-Fri 8:30 AM - 5:00 PM; Sat 9:00 AM - 1:00 PM; Sun Closed
Geographic Map & Coordinates
31.8000, -100.4000Adjacent & Contiguous ZIP Codes
Nearby postal codes bordering 78666 in San Marcos
Frequently Asked Questions About 78666 (San Marcos, TX)
What county is ZIP code 78666 located in for tax and voter purposes? ▾
ZIP code 78666 is located within Hays County, Texas. The official county seat is San Marcos, and the primary jurisdiction carries Texas FIPS code 48209.
What is the 4-digit ZIP+4 code for 78666? ▾
The full 9-digit postal code format is 78666-XXXX, where the last 4 digits specify exact delivery routes, high-rise buildings, or street blocks. For regular mail and parcel shipping, the 5-digit code 78666 is fully valid, while specific ZIP+4 extensions can be verified with USPS address validation.
Where is the nearest USPS post office for 78666 and what are the lobby hours? ▾
The primary USPS facility serving 78666 is USPS Post Office - San Marcos, located at 100 Main St, San Marcos, TX 78666. Retail lobby operations run during Mon-Fri 8:30 AM - 5:00 PM; Sat 9:00 AM - 1:00 PM; Sun Closed. Contact inquiries can be made at (800) 275-8777.
What telephone area codes and time zone apply to 78666? ▾
ZIP code 78666 is located in the America/Chicago (CST / CDT) time zone (observing Daylight Saving Time). Telephone numbers in this area use area code(s) 512, 737 with mandatory 10-digit dialing.
What is the population and median household income for 78666? ▾
According to U.S. Census Bureau ACS data, ZIP code 78666 in San Marcos has an estimated population of 67,553 residents and a median household income of $93,840 per year (compared to the Texas state median of $74,640).
What postal codes border 78666 in San Marcos? ▾
Adjacent and contiguous ZIP codes bordering 78666 include 76066 (Millsap, ~0 mi), 75156 (Enchanted Oaks, ~48.3 mi), 75065 (Hickory Creek, ~60.1 mi), 78065 (Panhandle, ~60.1 mi).