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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/21231

21231

ZIP 21231 is in Baltimore, Maryland, in Baltimore City; area codes 410, 443 and 667; Eastern time. Baltimore has 42 ZIP codes in all.

Type
Standard
Time zone
America/New_York
Population
14,969
Coordinates
39.2885, -76.5920
☼ Live from 21231 — Baltimore, MD

Weather right now

Asking the National Weather Service…

NEXRAD radar
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Local time: —

Where 21231 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 21231
  • 🔢 Type 21231 into a pocket calculator and turn it upside down: IEZIZ — not quite a word, sorry.
  • ➕ As a number, 21,231 = 3 × 3 × 7 × 337. Its digits add up to 9, a total 375 other ZIP codes share.
  • 💾In binary, the way a computer stores it: 101001011101111
  • 🏠 Its numerical neighbours: 21230 (Baltimore, MD, 2 mi away) and 21233 (Baltimore, MD, 1 mi away).
  • 🔄 Backwards, 21231 becomes 13212 — and that is a real ZIP code: Syracuse, NY, 266 miles away.
  • 👥 17 other ZIP codes are made of exactly the same digits (11223, 11232, 12123, 12132, 12231, 13122, …). The farthest-flung twin is 32121 in Daytona Beach, FL, 741 miles away.
  • 🧭 Farther north than 51% of all ZIP codes, and farther east than 83%.
  • 🎯1,169 miles east of the geographic center of the Lower 48, near Lebanon, Kansas.
  • 🌏 Dig straight through the Earth from 21231 and you would come out at 39.29°S, 103.41°E — 862 miles from Perth, Australia, the nearest big city to that spot.
  • ☀Longest day of the year: 14h 56m of daylight. Shortest: 9h 24m.
  • 📏 At 0.867 square miles of land, 21231 is bigger than 7% of ZIP codes — about 420 football fields.
🌙 The sky over 21231 today
  • Working out the sun…
🌋 Shake report
  • Checking the USGS…

Source: USGS.

People and housing

Population14,969This ZIP14,969
Households8,136This ZIP8,136
Housing units9,514This ZIP9,514
Median age32.7This ZIP32.7Maryland39.4US 38.9
Median household income$85,254This ZIP$85,254Maryland$103,678US $80,734
Median home value$350,100This ZIP$350,100Maryland$419,900US $332,700
Median gross rent$1,796This ZIP$1,796Maryland$1,705US $1,413
Bachelor's degree or higher64.3%This ZIP64.3%
Mean commute24.1 minThis ZIP24.1 min
Population density17,265.3 / sq miThis ZIP17,265.3 / sq mi

Business and tax activity

Business establishments509This ZIP509
Employees9,784This ZIP9,784
Annual payroll$981,825,000This ZIP$981,825,000
Tax returns filed8,200This ZIP8,200
Total adjusted gross income$830,214,000This ZIP$830,214,000

Land area

Land area0.87 sq miThis ZIP0.87 sq mi
Water area0.08 sq miThis ZIP0.08 sq mi

Other place names in 21231

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

ZIP codes near 21231

ZIPCityDistance
21233 Baltimore, MD 0.7 mi
21287 Baltimore, MD 0.8 mi
21202 Baltimore, MD 1.0 mi
21203 Baltimore, MD 1.5 mi
21235 Baltimore, MD 1.5 mi
21241 Baltimore, MD 1.5 mi
21263 Baltimore, MD 1.5 mi
21264 Baltimore, MD 1.5 mi
21270 Baltimore, MD 1.5 mi
21273 Baltimore, MD 1.5 mi

Find every ZIP code within 10 miles of 21231 →

Questions about this ZIP code

Where is ZIP code 21231?

21231 is in Baltimore, Maryland, in Baltimore city, part of the Baltimore-Columbia-Towson, MD metropolitan area. Its published point location is 39.2885, -76.5920.

What county is 21231 in?

21231 lies in Baltimore city.

What area code is 21231?

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

What time zone is 21231 in?

21231 uses America/New_York.

How many people live in 21231?

About 14,969 people live in ZIP code 21231, in 8,136 households, at 17,265.3 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 21231?

$85,254 a year, against $103,678 across Maryland.

What ZIP codes are near 21231?

The closest are 21233 (0.7 mi), 21287 (0.8 mi), 21202 (1 mi), 21203 (1.5 mi) and 21235 (1.5 mi).

Is 21231 a PO Box ZIP code?

21231 is a standard ZIP code. A normal ZIP code with street delivery.

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Cite this page

zipcodes.pro. “21231 ZIP Code — Baltimore, Maryland (Baltimore City).” Data release 2026-10-12. Retrieved 2026-10-20. https://zipcodes.pro/zip/21231

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