ZIP Code 21231 — Baltimore, MD
21231 is a standard (street delivery) ZIP code serving Baltimore, Maryland, in Baltimore 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 21231 at a glance
| ZIP code | 21231 |
|---|---|
| Primary city | Baltimore |
| State | Maryland (MD) |
| County | Baltimore FIPS 24510 |
| ZIP type | Standard (street delivery) |
| Time zone | America/New_York |
| Population | 14,969 |
| Coordinates | 39.287750, -76.592000 |
How ZIP+4 works in 21231
The four digits after the hyphen encode a delivery segment inside 21231. 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 21231 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.
Other ZIP codes in Baltimore
Nearby ZIP codes
Showing the closest twelve. See every ZIP code within 25 miles of 21231.
| ZIP | City | Distance |
|---|---|---|
| 21233 | Baltimore, MD | 0.8 mi |
| 21287 | Baltimore, MD | 0.8 mi |
| 21202 | Baltimore, MD | 1 mi |
| 21201 | Baltimore, MD | 1.7 mi |
| 21205 | Baltimore, MD | 1.8 mi |
| 21213 | Baltimore, MD | 2 mi |
| 21230 | Baltimore, MD | 2.2 mi |
| 21224 | Baltimore, MD | 2.7 mi |
| 21217 | Baltimore, MD | 2.8 mi |
| 21218 | Baltimore, MD | 3 mi |
| 21223 | Baltimore, MD | 3.3 mi |
| 21211 | Baltimore, MD | 3.8 mi |
Questions about 21231
What is the ZIP+4 code for 21231?
21231 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 21231, you need to look up a specific street address to get them.
What city is 21231?
21231 is assigned to Baltimore, Maryland, in Baltimore 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.