ZIP Code 21555 — Oldtown, MD
21555 is a standard (street delivery) ZIP code serving Oldtown, Maryland, in Allegany 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 21555 at a glance
| ZIP code | 21555 |
|---|---|
| Primary city | Oldtown |
| State | Maryland (MD) |
| County | Allegany FIPS 24001 |
| ZIP type | Standard (street delivery) |
| Time zone | America/New_York |
| Population | 1,470 |
| Coordinates | 39.587770, -78.556850 |
How ZIP+4 works in 21555
The four digits after the hyphen encode a delivery segment inside 21555. 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 21555 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 21555.
| ZIP | City | Distance |
|---|---|---|
| 25431 | Levels, WV | 7 mi |
| 21530 | Flintstone, MD | 7 mi |
| 26722 | Green Spring, WV | 7.5 mi |
| 21560 | Spring Gap, MD | 8.1 mi |
| 21766 | Little Orleans, MD | 9.8 mi |
| 26763 | Springfield, WV | 10.4 mi |
| 25434 | Paw Paw, WV | 10.6 mi |
| 25444 | Slanesville, WV | 10.7 mi |
| 25422 | Great Cacapon, WV | 10.7 mi |
| 26767 | Wiley Ford, WV | 10.8 mi |
| 21502 | Cumberland, MD | 11.2 mi |
| 25437 | Points, WV | 11.5 mi |
Questions about 21555
What is the ZIP+4 code for 21555?
21555 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 21555, you need to look up a specific street address to get them.
What city is 21555?
21555 is assigned to Oldtown, Maryland, in Allegany 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.