ZIP Code 51040 — Onawa, IA
51040 is a standard (street delivery) ZIP code serving Onawa, Iowa, in Monona 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 51040 at a glance
| ZIP code | 51040 |
|---|---|
| Primary city | Onawa |
| State | Iowa (IA) |
| County | Monona FIPS 19133 |
| ZIP type | Standard (street delivery) |
| Time zone | America/Chicago |
| Population | 3,500 |
| Coordinates | 42.030730, -96.070600 |
How ZIP+4 works in 51040
The four digits after the hyphen encode a delivery segment inside 51040. 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 51040 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 51040.
| ZIP | City | Distance |
|---|---|---|
| 51523 | Blencoe, IA | 8.2 mi |
| 51010 | Castana, IA | 8.8 mi |
| 51063 | Whiting, IA | 9.1 mi |
| 68020 | Decatur, NE | 10.2 mi |
| 51051 | Rodney, IA | 13 mi |
| 51558 | Moorhead, IA | 13 mi |
| 51545 | Little Sioux, IA | 13.5 mi |
| 51572 | Soldier, IA | 14.6 mi |
| 51026 | Hornick, IA | 15 mi |
| 68039 | Macy, NE | 15.1 mi |
| 51056 | Smithland, IA | 15.3 mi |
| 51055 | Sloan, IA | 15.8 mi |
Questions about 51040
What is the ZIP+4 code for 51040?
51040 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 51040, you need to look up a specific street address to get them.
What city is 51040?
51040 is assigned to Onawa, Iowa, in Monona 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.