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zipcodes.pro — ZIP/78666

78666

ZIP 78666 is in San Marcos, Texas, mostly in Hays County; area codes 512 and 737; Central time. San Marcos has 2 ZIP codes; the other is 78667.

Type
Standard
Time zone
America/Chicago
County
Hays +3 more
Population
88,583
Coordinates
29.8817, -97.9848
☼ Live from 78666 — San Marcos, TX

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Where 78666 is

Approximate ZIP boundary (Census ZCTA 2020). ZIP codes are mail routes, not areas, so the shape shown is the Census tabulation area that approximates it.

★ Weird and wonderful facts about 78666
  • 🔢 Type 78666 into a pocket calculator and turn it upside down: gggBL — not quite a word, sorry.
  • ➕ As a number, 78,666 = 2 × 3 × 7 × 1873. Its digits add up to 33, a total 456 other ZIP codes share.
  • 💾In binary, the way a computer stores it: 10011001101001010
  • 🏠 Its numerical neighbours: 78665 (Round Rock, TX, 51 mi away) and 78667 (San Marcos, TX, 12 mi away).
  • 🔄 Backwards, 78666 becomes 66687, which is not a ZIP code at all.
  • 👥 4 other ZIP codes are made of exactly the same digits (68667, 68766, 76686, 76866). The farthest-flung twin is 68766 in Page, NE, 867 miles away.
  • 🧭 Farther south than 93% of all ZIP codes, and farther west than 77%.
  • 🎯688 miles south of the geographic center of the Lower 48, near Lebanon, Kansas.
  • 🌏 Dig straight through the Earth from 78666 and you would come out at 29.88°S, 82.02°E — 1,480 miles from Port-aux-Français, French Southern Territories, the nearest big city to that spot.
  • ☀Longest day of the year: 14h 04m of daylight. Shortest: 10h 13m.
  • 📏 At 192.4 square miles of land, 78666 is bigger than 90% of ZIP codes — room for about 146 Central Parks.
🌙 The sky over 78666 today
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🌋 Shake report
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Source: USGS.

People and housing

Population88,583This ZIP88,583
Households33,949This ZIP33,949
Housing units36,580This ZIP36,580
Median age26.9This ZIP26.9Texas35.6US 38.9
Median household income$54,737This ZIP$54,737Texas$78,476US $80,734
Median home value$306,700This ZIP$306,700Texas$283,800US $332,700
Median gross rent$1,319This ZIP$1,319Texas$1,403US $1,413
Bachelor's degree or higher35.7%This ZIP35.7%
Mean commute25.5 minThis ZIP25.5 min
Population density460.5 / sq miThis ZIP460.5 / sq mi

Business and tax activity

Business establishments1,880This ZIP1,880
Employees34,315This ZIP34,315
Annual payroll$1,555,086,000This ZIP$1,555,086,000
Tax returns filed36,290This ZIP36,290
Total adjusted gross income$2,365,948,000This ZIP$2,365,948,000

Land area

Land area192.36 sq miThis ZIP192.36 sq mi
Water area1.01 sq miThis ZIP1.01 sq mi

Counties 78666 spans

A ZIP code is a mail route and ignores county lines. Shares are by overlapping land area.

CountyShare of this ZIP
Hays County 77.9%
Guadalupe County 15.7%
Comal County 4.3%
Caldwell County 2.0%

Other place names in 78666

Census places whose land this ZIP code overlaps. The Postal Service may accept other city names in an address, too.

ZIP codes near 78666

ZIPCityDistance
78655 Martindale, TX 10.1 mi
78656 Maxwell, TX 10.7 mi
78670 Staples, TX 11.5 mi
78667 San Marcos, TX 12.0 mi
78640 Kyle, TX 12.5 mi
78130 New Braunfels, TX 13.9 mi
78622 Fentress, TX 14.1 mi
78623 Fischer, TX 14.8 mi
78131 New Braunfels, TX 14.9 mi
78135 New Braunfels, TX 14.9 mi

Find every ZIP code within 10 miles of 78666 →

Questions about this ZIP code

Where is ZIP code 78666?

78666 is in San Marcos, Texas, in Hays County, part of the Austin-Round Rock-San Marcos, TX metropolitan area. Its published point location is 29.8817, -97.9848.

What county is 78666 in?

78666 spans 4 counties: Hays County, Guadalupe County, Comal County and Caldwell County. Most of it falls in Hays County, measured by overlapping land area — the county holding the most land in a ZIP code is not always the one holding the most residents.

What area code is 78666?

San Marcos uses area codes 512 and 737, from NANPA's telephone records.

What time zone is 78666 in?

78666 uses America/Chicago.

How many people live in 78666?

About 88,583 people live in ZIP code 78666, in 33,949 households, at 460.5 people per square mile. These are American Community Survey 5-year estimates for the ZIP Code Tabulation Area, not a headcount.

What is the median household income in 78666?

$54,737 a year, against $78,476 across Texas.

What ZIP codes are near 78666?

The closest are 78655 (10.1 mi), 78656 (10.7 mi), 78670 (11.5 mi), 78667 (12 mi) and 78640 (12.5 mi).

Is 78666 a PO Box ZIP code?

78666 is a standard ZIP code. A normal ZIP code with street delivery.

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Cite this page

zipcodes.pro. “78666 ZIP Code — San Marcos, Texas (Hays County).” Data release 2026-10-12. Retrieved 2026-10-20. https://zipcodes.pro/zip/78666

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