What city is 21771 in?

21771 is a Mount Airy, MD mailing address. By land area, 7% lies inside Green Valley and 5% lies inside Mount Airy; the rest is outside any Census-defined city or community.

What is the population of 21771?

About 33,031 people (±2,079), according to the Census Bureau's American Community Survey 5-year estimates for 2020–2024. The 2020 Census counted 30,697.

What is the median household income in 21771?

$157,302 (±$7,190), compared with $103,678 for Maryland as a whole. Half the households in the ZIP code earn more and half earn less.

How many carrier routes and mailboxes are in 21771?

20 USPS carrier routes with 11,089 residential and 507 business mailboxes (11,600 in all), from the route data stored by EDDM2GO. An EDDM mailing can target any combination of these routes.

What ZIP codes are near 21771?

The closest, measured center to center: 21770 (6.1 mi, Green Valley), 21774 (6.3 mi, Linganore), 21797 (6.5 mi, Lisbon), 20872 (7.1 mi, Damascus), 21762 (7.6 mi, Libertytown) and 21776 (9.1 mi, New Windsor).

21771 ZIP Code, Mount Airy, MD

Q: What county is 21771 in?

21771 is mostly in Frederick County (51% of its land), with smaller parts in Carroll, Howard and Montgomery counties.

21771 is a ZIP code in Mount Airy, Maryland — mostly in Frederick County (51% of its land), with smaller parts in Carroll, Howard and Montgomery counties. It covers 90 square miles of land. The closest ZIP codes are 21770, 21774 and 21797. 33,031 people live here in 11,226 households. With about 369 people per square mile it is lightly settled, and most homes are owner-occupied (94%). Median household income is $157,302, well above the Maryland median of $103,678.

Quick facts

Mailing city: Mount Airy, MD
County: Frederick County
Land area: 90 sq mi
Population: 33,031
Median household income: $157,302
Carrier routes: 20 (11,089 homes)

Key figures

Measure	Value
Residents	33,031
Households	11,226
Median household income	$157,302
Income per person	$60,220
Median age	40.9
Homeowners	94.0%
Median home value	$556,200
Median rent	$2,252
Bachelor's degree or higher	48.8%
Average commute (minutes)	36.1
Households with kids under 18	35.1%
Moved in the past year	9.7%
Below the poverty line	3.1%
Broadband internet	95.0%
Speak a non-English language at home	10.9%

Household income

% of households	Value
<$10K	2.3%
$10–15K	0.6%
$15–25K	1.8%
$25–35K	2.1%
$35–50K	3.7%
$50–75K	7.4%
$75–100K	10.6%
$100–150K	18.0%
$150–200K	19.3%
$200K+	34.2%

Age

% of all residents	Value
<10	14.6%
10–19	11.6%
20–24	5.2%
25–34	9.9%
35–44	13.0%
45–54	13.2%
55–64	16.9%
65–74	9.4%
75+	6.2%

Tenure

% of housing units	Value
Owned, with mortgage	66.3%
Owned outright	23.6%
Rented	5.6%
Vacant	4.5%

Type of building

% of housing units	Value
Detached house	88.3%
Townhome	9.4%
2–4 units	0.6%
5–19 units	0.0%
20+ units	0.3%
Mobile / other	1.3%

Businesses in 21771

759 business establishments with 7,538 employees (ZIP Codes Business Patterns 2023).

Construction: 182
Professional, Scientific, and Technical Services: 95
Other Services (except Public Administration): 72
Administrative and Support and Waste Management and Remediation Services: 71
Health Care and Social Assistance: 71
Retail Trade: 70
Accommodation and Food Services: 48
Real Estate and Rental and Leasing: 38

EDDM carrier routes

21771 has 20 USPS carrier routes with 11,089 residential and 507 business mailboxes. Open the EDDM route map.

Carrier routes in 21771

21771 has 20 USPS carrier routes (20 rural (R)) with 11,089 residential and 507 business mailboxes. Routes range from 295 homes (R424) to 687 homes (R022); the median route has 556 homes. The Census counted 11,226 households in 21771 (2020–2024 average); USPS counts current mailboxes, including new and vacant homes.

Homes per route	Routes
1–249	0
250–499	4
500–749	16
750–999	0
1,000–1,499	0
1,500+	0

Best routes in 21771 for…

Most businesses

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

Route R424 — USPS business mailboxes 104, 295 homes
Route R023 — USPS business mailboxes 89, 445 homes
Route R012 — USPS business mailboxes 76, 560 homes
Route R015 — USPS business mailboxes 49, 572 homes
Route R022 — USPS business mailboxes 47, 687 homes

Select these 5 routes on the route map

Every carrier route in 21771

Route	Type	Homes	Businesses	Est. median income	Est. owners	Est. families with kids	Est. moved in past year
R001	Rural	602	3	$176,581	—	—	—
R002	Rural	580	7	$132,032	—	—	—
R003	Rural	522	4	$130,993	—	—	—
R004	Rural	534	13	$156,747	—	—	—
R005	Rural	605	15	$200,001+	—	—	—
R006	Rural	654	46	$96,702	—	—	—
R007	Rural	552	2	$154,466	—	—	—
R009	Rural	549	8	$137,019	—	—	—
R010	Rural	650	1	$121,699	—	—	—
R011	Rural	499	5	$167,025	—	—	—
R012	Rural	560	76	$200,001+	—	—	—
R015	Rural	572	49	$184,908	—	—	—
R016	Rural	493	4	$154,542	—	—	—
R018	Rural	550	2	$200,001+	—	—	—
R019	Rural	626	30	$121,912	—	—	—
R020	Rural	515	1	$132,032	—	—	—
R021	Rural	599	1	$154,466	—	—	—
R022	Rural	687	47	$200,001+	—	—	—
R023	Rural	445	89	$154,542	—	—	—
R424	Rural	295	104	$96,702	—	—	—

Income, owners, families and movers are estimates for each route (how we estimate them); mailbox counts are current USPS figures. Open 21771 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

21770 — Green Valley CDP, MD (6.1 mi)
21774 — Linganore CDP, MD (6.3 mi)
21797 — Lisbon CDP, MD (6.5 mi)
20872 — Damascus CDP, MD (7.1 mi)
21762 — Libertytown CDP, MD (7.6 mi)
21776 — New Windsor town, MD (9.1 mi)
21723 (9.5 mi)
21754 — Urbana CDP, MD (9.5 mi)

Areas that include 21771

Green Valley, MD ZIP codes — 3 ZIP codes
Mount Airy, MD ZIP codes — 1 ZIP code
Carroll County ZIP codes — 14 ZIP codes
Frederick County ZIP codes — 33 ZIP codes
Howard County ZIP codes — 24 ZIP codes
Maryland ZIP code data

Where it ranks

Mail every home in 21771

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) 21771, which approximates the USPS ZIP code area. Census figures: American Community Survey 5-year estimates, 2020–2024.

Frequently asked questions

What city is 21771 in?: 21771 is a Mount Airy, MD mailing address. By land area, 7% lies inside Green Valley and 5% lies inside Mount Airy; the rest is outside any Census-defined city or community.
What county is 21771 in?: 21771 is mostly in Frederick County (51% of its land), with smaller parts in Carroll, Howard and Montgomery counties.
What is the population of 21771?: About 33,031 people (±2,079), according to the Census Bureau's American Community Survey 5-year estimates for 2020–2024. The 2020 Census counted 30,697.
What is the median household income in 21771?: $157,302 (±$7,190), compared with $103,678 for Maryland as a whole. Half the households in the ZIP code earn more and half earn less.
How many carrier routes and mailboxes are in 21771?: 20 USPS carrier routes with 11,089 residential and 507 business mailboxes (11,600 in all), from the route data stored by EDDM2GO. An EDDM mailing can target any combination of these routes.
What ZIP codes are near 21771?: The closest, measured center to center: 21770 (6.1 mi, Green Valley), 21774 (6.3 mi, Linganore), 21797 (6.5 mi, Lisbon), 20872 (7.1 mi, Damascus), 21762 (7.6 mi, Libertytown) and 21776 (9.1 mi, New Windsor).

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