ZIP Code 57421 — Amherst, SD
57421 is a standard (street delivery) ZIP code serving Amherst, South Dakota, in Marshall 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 57421 at a glance
| ZIP code | 57421 |
|---|---|
| Primary city | Amherst |
| State | South Dakota (SD) |
| County | Marshall FIPS 46091 |
| ZIP type | Standard (street delivery) |
| Time zone | America/Chicago |
| Population | 75 |
| Coordinates | 45.750450, -97.906180 |
How ZIP+4 works in 57421
The four digits after the hyphen encode a delivery segment inside 57421. 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 57421 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 57421.
| ZIP | City | Distance |
|---|---|---|
| 57432 | Claremont, SD | 7.3 mi |
| 57430 | Britton, SD | 10.1 mi |
| 57454 | Langford, SD | 11.6 mi |
| 57449 | Houghton, SD | 13 mi |
| 57446 | Hecla, SD | 14.4 mi |
| 57468 | Pierpont, SD | 18.9 mi |
| 58017 | Cogswell, ND | 20.3 mi |
| 57433 | Columbia, SD | 21.3 mi |
| 57247 | Lake City, SD | 21.7 mi |
| 57422 | Andover, SD | 22.6 mi |
| 57445 | Groton, SD | 22.7 mi |
| 58043 | Havana, ND | 23.7 mi |
Questions about 57421
What is the ZIP+4 code for 57421?
57421 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 57421, you need to look up a specific street address to get them.
What city is 57421?
57421 is assigned to Amherst, South Dakota, in Marshall 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.