ZIP Code 57646 — Mound City, SD
57646 is a standard (street delivery) ZIP code serving Mound City, South Dakota, in Campbell 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 57646 at a glance
| ZIP code | 57646 |
|---|---|
| Primary city | Mound City |
| State | South Dakota (SD) |
| County | Campbell FIPS 46021 |
| ZIP type | Standard (street delivery) |
| Time zone | America/Chicago |
| Population | 272 |
| Coordinates | 45.687530, -100.053950 |
How ZIP+4 works in 57646
The four digits after the hyphen encode a delivery segment inside 57646. 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 57646 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 57646.
| ZIP | City | Distance |
|---|---|---|
| 57632 | Herreid, SD | 9.8 mi |
| 57631 | Glenham, SD | 13.4 mi |
| 57452 | Java, SD | 14 mi |
| 57472 | Selby, SD | 18 mi |
| 57648 | Pollock, SD | 20.9 mi |
| 57437 | Eureka, SD | 22 mi |
| 57428 | Bowdle, SD | 24.4 mi |
| 57658 | Wakpala, SD | 24.4 mi |
| 58542 | Hague, ND | 25.1 mi |
| 58581 | Zeeland, ND | 27.7 mi |
| 57420 | Akaska, SD | 28.1 mi |
| 58573 | Strasburg, ND | 31.1 mi |
Questions about 57646
What is the ZIP+4 code for 57646?
57646 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 57646, you need to look up a specific street address to get them.
What city is 57646?
57646 is assigned to Mound City, South Dakota, in Campbell 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.