ZIP Codes in Alton, IA
Alton uses 1 ZIP code, all in Sioux County. Pick one below for details, or look up the full nine-digit ZIP+4 for a specific street address.
All 1 Alton ZIP codes
| ZIP | Type | County | Population |
|---|---|---|---|
| 51003 | standard | Sioux | 1,938 |
Finding a ZIP+4 in Alton
Knowing which of these 1 ZIP codes covers an address only gets you partway. The four-digit extension identifies the specific delivery point — typically one side of one block. Two houses facing each other on the same Alton street almost always have different ZIP+4 codes even though they share all five leading digits.
Appending ZIP+4 to a mailing list?
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