ZIP Code 21770 — Monrovia, MD
21770 is a standard (street delivery) ZIP code serving Monrovia, Maryland, in Frederick County. To mail something here you only need these five digits — but the four-digit extension narrows delivery to a single point, and it is what USPS bulk postage discounts are priced on.
ZIP code 21770 at a glance
| ZIP code | 21770 |
|---|---|
| Primary city | Monrovia |
| State | Maryland (MD) |
| County | Frederick FIPS 24021 |
| ZIP type | Standard (street delivery) |
| Time zone | America/New_York |
| Population | 8,751 |
| Coordinates | 39.352450, -77.257910 |
How ZIP+4 works in 21770
The four digits after the hyphen encode a delivery segment inside 21770. In practice one segment usually means:
- One side of one block — odd numbers on a street between two cross streets
- A single large building, or one floor of it
- A group of PO boxes, sometimes a single box
- A single business that receives enough mail to warrant its own code
That is why 21770 has no single ZIP+4: two neighbors across the street from each other usually have different ones. Enter a street address above and we will return the exact nine-digit code along with the standardized USPS address format.
Nearby ZIP codes
Showing the closest twelve. See every ZIP code within 25 miles of 21770.
| ZIP | City | Distance |
|---|---|---|
| 21754 | Ijamsville, MD | 3 mi |
| 21774 | New Market, MD | 4 mi |
| 20872 | Damascus, MD | 4.8 mi |
| 21771 | Mount Airy, MD | 6.1 mi |
| 21704 | Frederick, MD | 6.2 mi |
| 20871 | Clarksburg, MD | 6.6 mi |
| 21701 | Frederick, MD | 7.7 mi |
| 21762 | Libertytown, MD | 8.9 mi |
| 21705 | Frederick, MD | 9 mi |
| 21717 | Buckeystown, MD | 9.3 mi |
| 21797 | Woodbine, MD | 10.1 mi |
| 20876 | Germantown, MD | 10.1 mi |
Questions about 21770
What is the ZIP+4 code for 21770?
21770 is the five-digit ZIP code. The ZIP+4 adds four more digits that identify a specific delivery point — usually one side of a city block, a single building, or a group of PO boxes. Because those four digits change from address to address within 21770, you need to look up a specific street address to get them.
What city is 21770?
21770 is assigned to Monrovia, Maryland, in Frederick County.
Do I need to use the ZIP+4?
It is optional for ordinary mail, but it speeds up sorting and it is required for most USPS bulk-mail postage discounts. Many address-verification and e-commerce systems also use ZIP+4 to confirm a delivery point exists.
Need thousands of these?
Upload a CSV and get ZIP+4, county, carrier route, and delivery-point data appended to every row — or call the API directly.