Residential delivery area · Texas
ZIP Code 78666: San Marcos, TX
ZIP code 78666 uses the postal name San Marcos, Texas and lies mostly in Hays County (78% of its land), reaching into Guadalupe County, Comal County and Caldwell County (Census 2020 ZIP-county file). About 89,000 people live there (Census Bureau, ACS 2020-2024). Median household income is $54,737 (Census Bureau, ACS 2020-2024). By Census place, its land lies in San Marcos (17%) and Redwood (3%), and 5% in smaller places; 75% is outside any Census place.
- ACS2020-24
- Census2020
- FHFA2025
- ZBP2023
- IRS2022
- Town
- San Marcos · its only residential ZIP
- County
- Hays County (78%); Guadalupe County (16%); Comal County (4%); Caldwell County (2%)
- Census places
- San Marcos (17%); Redwood (3%) census-designated place
- Metro area
- Austin-Round Rock-San Marcos, TX
- House districts
- TX-21 (58%), TX-35 (24%), TX-15 (16%), TX-27 (2%) 119th Congress, by share of land
- State
- Texas
- Time zone
- Central
- Land area
- 192.4 sq mi · 461 people per sq mi
- PO Box ZIPs
- 78667 also use the name San Marcos
Where is ZIP code 78666?
78666 centers on 29.882°, -97.985° and covers 192.4 square miles of land plus 1.0 of water. It borders 11 ZIP codes: 78655, 78656, 78670, 78640, 78130, 78623, 78132, 78676, 78133, 78638 and more.
The map draws ZIP code areas only. For the streets inside 78666, open its center on OpenStreetMap.
Source: U.S. Census Bureau, 2020 ZCTA cartographic boundaries and the 2023 Gazetteer (2020 ZCTAs); ZIP-to-county shares, Census places and House districts (119th Congress) from the Census 2020 relationship files (shares of land); metro area from the OMB delineation (July 2023); town name and time zone from simplemaps US ZIP Codes (CC BY 4.0).
How does 78666 compare with the rest of Hays County?
| Measure | 78666 | In Hays County | In TX |
|---|---|---|---|
| People (ACS 2020-2024) | 88,583 | 1st of 13 | 19th of 1,990 |
| Median household income | $55k | 9th of 9 | 964th of 1,172 |
| Median home value | $307k | 11th of 11 | 372nd of 1,172 |
Its median household income is higher than in 21% of U.S. residential ZIP codes, and it is denser than 71% of all U.S. residential ZIP codes. ZIP codes at the ACS caps ($250,000 or more for household income, $2,000,000 or more for home value) share the top rank.
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates (B01003, B19013, B25077); ranks by PlainZIP over residential ZIP codes (ZCTAs).
How many people live in 78666?
The 2020 Census counted 86,584 people in 78666; the ACS, which samples households over 2020-2024, estimates 88,583. Its boundary changed between the 2010 and 2020 censuses, so the two counts are not compared.
- People, ACS 2020-2024
- 88,583
- 2020 Census count
- 86,584
- Households
- 33,949
- Median age
- 26.9
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates (B01003, B01002, B11001); 2020 Census (DHC P1); 2010 Census (SF1 P1).
Who lives in 78666?
Of the 88,583 people the ACS estimates in 78666, 14.2% are under 18 and 12.0% are 65 or older. The largest group by race and Hispanic origin is Hispanic or Latino (44.3%), then White (not Hispanic) (43.9%).
- Under 1814.2%
- 18 to 6473.8%
- 65 and older12.0%
- Hispanic or Latino44.3%
- White, not Hispanic43.9%
- Other or two or more5.2%
- Black, not Hispanic4.9%
- Asian, not Hispanic1.7%
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates (B01001 age by sex, B03002 Hispanic or Latino origin by race); shares of the estimated population, small ZIP codes carry wide margins.
What do households in 78666 earn?
Median household income is $54,737 (ACS 2020-2024), the 9th highest of the 9 ranked ZIP codes in Hays County.
- Median household income
- $54,737
- Income per person
- $29,465
- Below the poverty line
- 23.8%
- Unemployed (of the labor force)
- 5.2%
- Adults 25+ with a bachelor's degree
- 35.7%
- Adjusted gross income per tax return, 2022
- $65,19636,290 returns; wages 66% of AGI (IRS)
Source: U.S. Census Bureau, ACS 2020-2024 and 2015-2019 5-year estimates (B19013, B19301, B17001, B23025, B15003; 2015-2019 dollars converted with the BLS CPI-U, 1.22699); IRS Statistics of Income, ZIP code data, tax year 2022 (adjusted gross income per return, filed under the address on the return).
What are homes worth in 78666?
FHFA's house price index for 78666, built from repeat sales and appraisals of the same homes, rose 88% from 2015 to 2025 and rose 41% from 2020 to 2025, and moved −1.7% in 2025.
- Median home value (owners' estimate)
- $306,700
- Median gross rent
- $1,319
- Homes owned by their occupants
- 38.1%
- Housing units
- 36,580
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates (B25077, B25064, B25003, B25001); FHFA House Price Index, annual five-digit ZIP, updated 2026-03-31.
What businesses are in 78666?
1,880 business establishments had a location in this ZIP code in 2023, 180 more than in 2018; the most are in retail trade (ZIP Code Business Patterns).
- Retail trade393
- Accommodation and food services279
- Health care and social assistance189
- Other services (except public administration)148
- Construction141
- Professional, scientific, and technical services141
Source: U.S. Census Bureau, ZIP Code Business Patterns 2023 and 2018 (establishments with paid employees, by the business's ZIP code).
Which ZIP codes are next to 78666?
| ZIP | Town | People | Household income | Distance |
|---|---|---|---|---|
| 78655 | Martindale | 3,730 | $56k | 10.1 mi |
| 78656 | Maxwell | 2,847 | $81k | 10.7 mi |
| 78670 | Staples | 130 | $79k | 11.5 mi |
| 78640 | Kyle | 77,531 | $90k | 12.5 mi |
| 78130 | New Braunfels | 104,009 | $83k | 13.9 mi |
| 78623 | Fischer | 1,645 | $117k | 14.8 mi |
| 78132 | New Braunfels | 40,953 | $135k | 15.0 mi |
| 78676 | Wimberley | 15,822 | $87k | 15.1 mi |
| 78133 | Canyon Lake | 21,959 | $84k | 16.0 mi |
| 78638 | Kingsbury | 2,135 | $69k | 19.5 mi |
| 78155 | Seguin | 55,600 | $71k | 24.0 mi |
| 78622 | Fentress | 331 | – | 14.1 mi (near) |
Source: PlainZIP from the Census 2020 ZCTA boundaries (shared edges) and internal points; figures ACS 2020-2024.
Which other ZIP codes use the name San Marcos?
1 more ZIP code carries the postal name San Marcos, TX without a residential delivery area: PO boxes at the post office, or a single organization with its own ZIP code. The Census Bureau publishes no figures for it.
| ZIP | County |
|---|---|
| 78667 | Hays County |
Source: GeoNames postal codes (CC BY 4.0), downloaded 2026-10-09; a ZIP code with no Census ZCTA has no residential delivery area.