Every ZIP code in the United States, with weather, radar, trivia and the numbers behind it. Five digits since 1963!

ZIP stands for Zone Improvement Plan. The codes went live on July 1, 1963.The lowest ZIP code is 00501 — the IRS in Holtsville, New York.The highest ZIP code is 99950, in Ketchikan, Alaska.Type 07734 into a calculator and turn it upside down: hELLO. It is Keansburg, New Jersey.12345 belongs to one company: General Electric in Schenectady, New York.The first digit is a region: 0 is New England and New Jersey, 9 is the West Coast, Alaska and Hawaii.Mr. ZIP, the cartoon mailman, was the mascot that sold the idea to America.ZIP+4 arrived in 1983 and can narrow a ZIP down to one side of one block.A ZIP code is a mail route, not a place: plenty of them cross county and even state lines.Play ZIP Hunt: guess the secret ZIP code of the day in six tries.
zipcodes.pro — ZIP/21104

21104

ZIP 21104 is Marriottsville, Maryland, mostly in Howard County; area codes 410, 443 and 667; Eastern time.

Type
Standard
Time zone
America/New_York
County
Howard +2 more
Population
6,052
Coordinates
39.3469, -76.9128
☼ Live from 21104 — Marriottsville, MD

Weather right now

Asking the National Weather Service…

NEXRAD radar
Finding the nearest radar…
Local time: —

Where 21104 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 21104
  • 🔢 Type 21104 into a pocket calculator and turn it upside down: hOIIZ — not quite a word, sorry.
  • ➕ As a number, 21,104 = 2 × 2 × 2 × 2 × 1319. Its digits add up to 8, a total 251 other ZIP codes share.
  • 💾In binary, the way a computer stores it: 101001001110000
  • 🏠 Its numerical neighbours: 21102 (Manchester, MD, 24 mi away) and 21105 (Maryland Line, MD, 29 mi away).
  • 🔄 Backwards, 21104 becomes 40112, which is not a ZIP code at all.
  • 👥 34 other ZIP codes are made of exactly the same digits (02114, 02141, 04112, 04211, 10124, 11024, …). The farthest-flung twin is 42101 in Bowling Green, KY, 542 miles away.
  • 🧭 Farther north than 51% of all ZIP codes, and farther east than 82%.
  • 🎯1,151 miles east of the geographic center of the Lower 48, near Lebanon, Kansas.
  • 🌏 Dig straight through the Earth from 21104 and you would come out at 39.35°S, 103.09°E — 879 miles from Perth, Australia, the nearest big city to that spot.
  • ☀Longest day of the year: 14h 57m of daylight. Shortest: 9h 23m.
  • 📏 At 17.1 square miles of land, 21104 is bigger than 35% of ZIP codes — room for about 13 Central Parks.
🌙 The sky over 21104 today
  • Working out the sun…
🌋 Shake report
  • Checking the USGS…

Source: USGS.

People and housing

Population6,052This ZIP6,052
Households2,097This ZIP2,097
Housing units2,204This ZIP2,204
Median age43.1This ZIP43.1Maryland39.4US 38.9
Median household income$191,804This ZIP$191,804Maryland$103,678US $80,734
Median home value$680,200This ZIP$680,200Maryland$419,900US $332,700
Median gross rent$1,384This ZIP$1,384Maryland$1,705US $1,413
Bachelor's degree or higher64.4%This ZIP64.4%
Mean commute31.9 minThis ZIP31.9 min
Population density354.9 / sq miThis ZIP354.9 / sq mi

Business and tax activity

Business establishments157This ZIP157
Employees1,322This ZIP1,322
Annual payroll$72,588,000This ZIP$72,588,000
Tax returns filed2,960This ZIP2,960
Total adjusted gross income$535,404,000This ZIP$535,404,000

Land area

Land area17.05 sq miThis ZIP17.05 sq mi
Water area0.81 sq miThis ZIP0.81 sq mi

Counties 21104 spans

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

CountyShare of this ZIP
Howard County 53.4%
Carroll County 31.9%
Baltimore County 14.7%

Other place names in 21104

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

ZIP codes near 21104

ZIPCityDistance
21163 Woodstock, MD 3.5 mi
21794 West Friendship, MD 4.4 mi
21042 Ellicott City, MD 4.9 mi
21723 Cooksville, MD 5.0 mi
21784 Sykesville, MD 5.0 mi
21133 Randallstown, MD 5.8 mi
21244 Windsor Mill, MD 7.3 mi
21136 Reisterstown, MD 7.3 mi
21738 Glenwood, MD 7.7 mi
21041 Ellicott City, MD 7.8 mi

Find every ZIP code within 10 miles of 21104 →

Questions about this ZIP code

Where is ZIP code 21104?

21104 is in Marriottsville, Maryland, in Howard County, part of the Baltimore-Columbia-Towson, MD metropolitan area. Its published point location is 39.3469, -76.9128.

What county is 21104 in?

21104 spans 3 counties: Howard County, Carroll County and Baltimore County. Most of it falls in Howard 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 21104?

Marriottsville uses area codes 410, 443 and 667, from NANPA's telephone records.

What time zone is 21104 in?

21104 uses America/New_York.

How many people live in 21104?

About 6,052 people live in ZIP code 21104, in 2,097 households, at 354.9 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 21104?

$191,804 a year, against $103,678 across Maryland.

What ZIP codes are near 21104?

The closest are 21163 (3.5 mi), 21794 (4.4 mi), 21042 (4.9 mi), 21723 (5 mi) and 21784 (5 mi).

Is 21104 a PO Box ZIP code?

21104 is a standard ZIP code. A normal ZIP code with street delivery.

Download or cite

Cite this page

zipcodes.pro. “21104 ZIP Code — Marriottsville, Maryland (Howard County).” Data release 2026-10-12. Retrieved 2026-10-20. https://zipcodes.pro/zip/21104

Machine-readable version of these facts:

curl https://zipcodes.pro/zip/21104.json

Underlying data is public domain or openly licensed — sources, vintages and licences.