🇺🇸 United States ZIP Code

STANDARD

78666

San Marcos

ZIP Code 78666 is a standard zip code serving San Marcos, San Marcos, Texas (TX), in Hays County, United States. It has an estimated population of 63,836 with a median household income of $33,827. The area falls within the America/Chicago timezone.

Median Household Income vs. National Average

Location

Country: 🇺🇸 United States
State / Province: Texas (TX)
County: Hays
City: San Marcos
Timezone: America/Chicago

Coordinates

Latitude: 29.875400
Longitude: -97.940400

Geographic Details

Land Area: 176.55 mi²
Water Area: 0.94 mi²
Population Density: 362.0 people per mi² (65th percentile)
Bounding Box: 30.013428°N, 29.727324°S, -97.848594°E, -98.151587°W

With 63,836 residents spread across 176.55 square miles, this area has a population density of 362.0 people per square mile.

Demographics

63,836

Population

95th percentile

$33,827

Median Income

15th percentile

$125,000

Median Home Value

50th percentile

176.55 mi²

Land Area

The median household income in 78666 is $33,827, and the median home value is $125,000. This is below the national average for household income.

Housing

24,433

Total Units

22,874

Occupied Units

93.6%

Occupancy Rate

Nearby ZIP Codes

Other zip codes in San Marcos, TX.

78667

San Marcos

Similar ZIP Codes in Texas

ZIP codes with similar median household income in Texas.

76444

De Leon

$35,833

77045

Houston

$36,952

75835

Crockett

$29,086

75551

Atlanta

$38,043

75847

Kennard

$36,968

75705

Tyler

$32,083

78753

Austin

$38,884

75227

Dallas

$37,720

Frequently Asked Questions

What information is available for each ZIP code?

Each ZIP code page shows city, state, county, geographic coordinates, timezone, population, median household income, median home value, housing units, land area, population density, commute time, educational attainment, area codes, and ZIP code type (Standard, PO Box, or Unique).

What are the different types of ZIP codes?

There are three types of ZIP codes: Standard (residential and commercial delivery areas), PO Box (assigned to post office box sections), and Unique (assigned to a single high-volume address like a government agency or large company). Standard ZIP codes are the most common.

How often is ZIP code data updated?

ZIP code assignments are updated quarterly by the USPS. Demographic data comes from the US Census Bureau's American Community Survey (ACS), which releases new 5-year estimates annually. ZipFYI updates its data to reflect the latest available information.

What is population density and why does it matter?

Population density measures the number of people per square mile in a ZIP code area. It helps identify urban vs. rural areas, affects real estate values, impacts service availability, and is used in market analysis. Dense urban ZIP codes may have 50,000+ people per square mile.

How are ZIP code boundaries determined?

ZIP code boundaries are determined by the USPS based on mail delivery routes, not political or geographic boundaries. They follow carrier routes and may cross city, county, or even state lines. Boundaries can change when the USPS reorganizes delivery operations.

What does median household income tell me about a ZIP code?

Median household income is the middle value when all household incomes in a ZIP code are sorted. Half of households earn more and half earn less. It is a better indicator of typical earnings than average income, which can be skewed by very high or very low outliers.