78666 ZIP Code, San Marcos, TX

78666 is a ZIP code in San Marcos, Texas — mostly in Hays County (78% of its land), with smaller parts in Guadalupe, Comal and Caldwell counties. It covers 192 square miles of land, centered about 30 miles southwest of downtown Austin. The closest ZIP codes are 78655, 78656 and 78670. 88,583 people live here in 33,949 households, which puts it among the most populous 1% of Texas ZIP codes. With about 461 people per square mile it is lightly settled, and most households rent (38% own). Median household income is $54,737, below the Texas median of $78,476; the median age is 26.9, younger than most ZIP codes.

Quick facts

Key figures

MeasureValue
Residents88,583
Households33,949
Median household income$54,737
Income per person$29,465
Median age26.9
Homeowners38.1%
Median home value$306,700
Median rent$1,319
Bachelor's degree or higher35.7%
Average commute (minutes)25.5
Households with kids under 1820.7%
Moved in the past year28.8%
Below the poverty line23.8%
Broadband internet86.4%
Speak a non-English language at home27.9%

Household income

% of householdsValue
<$10K9.5%
$10–15K4.6%
$15–25K7.2%
$25–35K10.1%
$35–50K13.3%
$50–75K20.9%
$75–100K11.3%
$100–150K13.3%
$150–200K4.6%
$200K+5.2%

Age

% of all residentsValue
<107.8%
10–1914.9%
20–2422.3%
25–3416.6%
35–4411.2%
45–547.2%
55–648.0%
65–747.7%
75+4.3%

Tenure

% of housing unitsValue
Owned, with mortgage19.3%
Owned outright16.3%
Rented57.3%
Vacant7.2%

Type of building

% of housing unitsValue
Detached house39.2%
Townhome4.0%
2–4 units10.5%
5–19 units16.5%
20+ units22.9%
Mobile / other6.9%

Businesses in 78666

1,880 business establishments with 34,315 employees (ZIP Codes Business Patterns 2023).

EDDM carrier routes

78666 has 43 USPS carrier routes with 40,618 residential and 2,420 business mailboxes. Open the EDDM route map.

Carrier routes in 78666

78666 has 43 USPS carrier routes (18 city (C), 23 rural (R), 2 highway contract (H)) with 40,618 residential and 2,420 business mailboxes. Routes range from 448 homes (C017) to 1,909 homes (R019); the median route has 901 homes. The Census counted 33,949 households in 78666 (2020–2024 average); USPS counts current mailboxes, including new and vacant homes.

Homes per routeRoutes
1–2490
250–4991
500–74913
750–99910
1,000–1,49916
1,500+3

Best routes in 78666 for…

Highest income

For bigger-ticket offers: remodeling, pools, financial planning, private schools.

  1. Route H073 — Est. median household income $136,306, 644 homes
  2. Route R012 — Est. median household income $115,053, 1,006 homes
  3. Route R017 — Est. median household income $97,191, 1,039 homes
  4. Route R008 — Est. median household income $90,942, 552 homes
  5. Route R014 — Est. median household income $84,983, 1,069 homes

Select these 5 routes on the route map

Often mailed by: Home services EDDM, Real estate EDDM postcards, Landscaping and lawn care mailers

Most families with kids

For tutoring, youth sports, pediatric dental, child care and family dining.

  1. Route R010 — Est. families with children under 18 52.1%, 745 homes
  2. Route R003 — Est. families with children under 18 42.4%, 887 homes
  3. Route R016 — Est. families with children under 18 41.5%, 882 homes
  4. Route R014 — Est. families with children under 18 36.8%, 1,069 homes
  5. Route C019 — Est. families with children under 18 35.3%, 903 homes

Select these 5 routes on the route map

Often mailed by: Dental practice EDDM, Healthcare and clinic mailers

Most homeowners

Owners decide on roofs, HVAC, lawns, solar and insurance; renters usually can't.

  1. Route R012 — Est. owner-occupied homes 91.1%, 1,006 homes
  2. Route H073 — Est. owner-occupied homes 90.8%, 644 homes
  3. Route R017 — Est. owner-occupied homes 88.0%, 1,039 homes
  4. Route R008 — Est. owner-occupied homes 82.0%, 552 homes
  5. Route R010 — Est. owner-occupied homes 81.2%, 745 homes

Select these 5 routes on the route map

Often mailed by: Roofing direct mail, HVAC postcards

Most new movers

New residents are still choosing a dentist, a gym and a lawn service.

  1. Route C003 — Est. residents who moved in the past year 45.7%, 1,160 homes
  2. Route C014 — Est. residents who moved in the past year 44.5%, 521 homes
  3. Route C013 — Est. residents who moved in the past year 41.7%, 1,078 homes
  4. Route C017 — Est. residents who moved in the past year 41.6%, 448 homes
  5. Route C009 — Est. residents who moved in the past year 40.7%, 1,437 homes

Select these 5 routes on the route map

Often mailed by: Restaurant EDDM menus and offers, Gym and fitness mailers

Newest homes

Newer subdivisions: landscaping, window treatments, fencing, security, home warranties.

  1. Route R012 — Est. homes built 2010 or later 74.3%, 1,006 homes
  2. Route R016 — Est. homes built 2010 or later 73.2%, 882 homes
  3. Route R023 — Est. homes built 2010 or later 53.8%, 555 homes
  4. Route H073 — Est. homes built 2010 or later 53.4%, 644 homes
  5. Route C011 — Est. homes built 2010 or later 50.1%, 901 homes

Select these 5 routes on the route map

Most businesses

For B2B offers: office supplies, cleaning, IT, catering and commercial services.

  1. Route R006 — USPS business mailboxes 426, 1,009 homes
  2. Route C014 — USPS business mailboxes 329, 521 homes
  3. Route C008 — USPS business mailboxes 165, 644 homes
  4. Route R020 — USPS business mailboxes 138, 1,329 homes
  5. Route C005 — USPS business mailboxes 105, 1,010 homes

Select these 5 routes on the route map

Every carrier route in 78666

RouteTypeHomesBusinessesEst. median incomeEst. ownersEst. families with kidsEst. moved in past year
C001City7646$63,73035.1%29.4%14.6%
C002City71542$50,11521.4%15.0%34.9%
C003City1,1606$49,90227.6%13.9%45.7%
C004City6469$60,51946.5%22.6%23.3%
C005City1,010105$45,14222.4%19.1%31.5%
C008City644165$59,11122.0%24.3%22.7%
C009City1,43774$45,56613.1%10.5%40.7%
C010City6734$60,52929.6%15.5%26.5%
C011City90151$49,93522.3%26.5%28.2%
C012City1,12115$51,45914.6%19.9%34.3%
C013City1,07847$32,97714.7%5.5%41.7%
C014City521329$33,96313.2%9.3%44.5%
C015City1,051102$41,47729.4%25.1%33.9%
C016City8773$69,11363.2%22.2%14.3%
C017City44860$39,51710.7%13.0%41.6%
C019City90370$53,64653.7%35.3%19.2%
C020City55027$54,53229.7%12.1%37.7%
C021City81554$53,99664.7%11.9%16.2%
H073Highway contract64421$136,30690.8%22.8%15.1%
H074Highway contract1,76554$72,47469.4%22.5%27.0%
R001Rural1,03128$68,07260.0%23.1%20.5%
R002Rural6820$79,61770.1%17.5%17.4%
R003Rural8876$83,45873.1%42.4%13.7%
R004Rural6390$50,40657.4%6.1%12.0%
R005Rural1,09766$56,15039.7%23.2%36.5%
R006Rural1,009426$43,5369.2%19.2%27.6%
R007Rural63736$66,28560.1%17.4%22.5%
R008Rural55258$90,94282.0%8.9%9.1%
R009Rural1,277100$51,43337.5%20.6%24.8%
R010Rural74553$72,08381.2%52.1%10.9%
R011Rural1,22475$74,02266.0%21.6%20.6%
R012Rural1,0061$115,05391.1%34.9%18.5%
R013Rural9289$58,53634.2%27.4%26.4%
R014Rural1,0691$84,98371.9%36.8%20.3%
R015Rural84045$70,62266.4%6.7%11.7%
R016Rural88232$74,33348.9%41.5%16.3%
R017Rural1,0393$97,19188.0%6.1%8.9%
R018Rural1,22421$64,54147.5%31.6%25.2%
R019Rural1,90922$45,71910.8%26.7%29.3%
R020Rural1,329138$55,42329.9%24.0%32.3%
R021Rural77851$66,31663.1%6.4%12.0%
R022Rural1,5564$68,86653.6%35.2%23.5%
R023Rural5551$59,26644.0%27.1%28.8%

Income, owners, families and movers are estimates for each route (how we estimate them); mailbox counts are current USPS figures. Open 78666 on the EDDM route map.

How route demographics are estimated

Mailbox counts come from USPS; demographics are estimates

The number of homes and businesses on each carrier route is the current USPS EDDM count. The Census Bureau does not publish figures for carrier routes, so income, homeownership, ages, families, movers and housing age on a route are EDDM2GO estimates built from Census block groups (neighborhood areas of roughly 600 to 3,000 people).

How a route gets its figures: the block-group length-share method

We trace each route's streets every 25 meters and record which block group each stretch falls in. The route's homes are spread along its streets in proportion to length, so a route with 60% of its street length in one block group is assumed to have 60% of its homes there. Each block group then contributes its Census counts in proportion to the share of its housing units that sit on the route (capped at the whole block group). Medians are recalculated from the combined income, home-value and age brackets, the way the Census Bureau computes them, not averaged.

Margins of error

Census survey figures carry a margin of error at 90% confidence; we carry it through the calculation and show it as ±. Our margins treat the route-to-block-group split as exact, so the real uncertainty is larger. Routes with fewer than 100 estimated households, large margins, or streets we could not place are flagged.

Different years

USPS mailbox counts are current. Census figures are 5-year averages for 2020–2024, so a new subdivision may have more homes on the route today than the Census counted. Use the route figures to compare routes with each other, not as an exact head count.

Why some routes show identical figures

Two routes that run through the same block group get the same percentages and medians, because the Census publishes one set of figures for the whole block group. Their mailbox counts still differ, and those are exact.

Route and mailbox counts: USPS EDDM route data. Route demographics: EDDM2GO estimates from U.S. Census Bureau American Community Survey 5-year block-group data (2020–2024) and 2024 cartographic block-group boundaries. This product uses the Census Bureau Data API but is not endorsed or certified by the Census Bureau.

Nearby ZIP codes

Areas that include 78666

Where it ranks

Mail every home in 78666

Route counts on this page price as Full Service 6.5 × 9 postcards: we print, bundle by carrier route and hand the mailing to USPS. Prefer to take it to the Post Office yourself? Print only costs less and you pay postage at drop-off.

EDDM guides

ZIP code statistics describe the Census ZIP Code Tabulation Area (ZCTA) 78666, which approximates the USPS ZIP code area. Census figures: American Community Survey 5-year estimates, 2020–2024.

Frequently asked questions

What city is 78666 in?
78666 is a San Marcos, TX mailing address. By land area, 17% lies inside San Marcos, 4% lies inside Kyle and 3% lies inside Redwood; the rest is outside any Census-defined city or community.
What county is 78666 in?
78666 is mostly in Hays County (78% of its land), with smaller parts in Guadalupe, Comal and Caldwell counties.
What is the population of 78666?
About 88,583 people (±1,333), according to the Census Bureau's American Community Survey 5-year estimates for 2020–2024. The 2020 Census counted 86,584.
What is the median household income in 78666?
$54,737 (±$3,230), compared with $78,476 for Texas as a whole. Half the households in the ZIP code earn more and half earn less.
How many carrier routes and mailboxes are in 78666?
43 USPS carrier routes with 40,618 residential and 2,420 business mailboxes (43,040 in all), from the route data stored by EDDM2GO. An EDDM mailing can target any combination of these routes.
What ZIP codes are near 78666?
The closest, measured center to center: 78655 (10.1 mi, Martindale), 78656 (10.7 mi, San Marcos), 78670 (11.5 mi, Staples), 78640 (12.5 mi, Kyle), 78130 (13.9 mi, New Braunfels) and 78622 (14.1 mi).

This product uses the Census Bureau Data API but is not endorsed or certified by the Census Bureau.