ZIP codes in O'Brien County

14 ZIPs touch O'Brien County, Iowa. The blue dashed line is the county border; orange ZIPs reach into it.

ZIP codes

cross the county line

19,142

people in these ZIPs

counties in IA

Most people

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O'Brien County ZIP list

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Questions people actually ask

How many ZIP codes are in O'Brien County, Iowa?

14 ZIP codes reach into O'Brien County. 11 of them are only partly in the county and also cover a neighboring county.

Which ZIP code in O'Brien County has the most people?

51201 (Sheldon) has about 6,430 residents, the most of any ZIP touching O'Brien County, in the Census Bureau’s ACS 2020–2024 estimates.

Can a ZIP code be in O'Brien County and another county?

Yes. ZIP codes follow mail routes, not county lines. Rows marked with a percentage show how much of that ZIP’s land is in O'Brien County. For one address, pin the exact spot on the ZIP finder to see its county.

Where does this list come from?

ZIP areas and their county overlaps come from the Census Bureau’s 2020 ZIP Code Tabulation Area to county relationship file. PO Box ZIPs have no area, so each is placed in the county of the ZIP area nearest the town it serves.

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Updated 2026-11-10 · Where the data comes from