51101 ZIP Code: Sioux City, Iowa
ZIP code 51101 covers Sioux City, Iowa. It sits in Woodbury County. Sioux City is covered by 9 ZIP codes in total, so 51101 is one delivery area within it rather than the whole city. A ZIP code is a US Postal Service mail route, not a boundary on a map, so it describes where post is delivered rather than an administrative area.
| ZIP code | 51101 |
|---|---|
| Place | Sioux City |
| State | Iowa (IA) |
| County or equivalent | Woodbury County |
| ZIP codes covering Sioux City | 9 |
| Phone area codes in Iowa | 5 |
| Country | United States |
ZIP codes near 51101
- 51105 Sioux Cityabout 1 mile
- 51103 Sioux Cityabout 2 miles
- 51104 Sioux Cityabout 2 miles
- 68776 South Sioux City, NEabout 2 miles
- 51106 Sioux Cityabout 3 miles
- 51108 Sioux Cityabout 4 miles
- 51109 Sioux Cityabout 4 miles
- 57049 North Sioux City, SDabout 6 miles
Distances are straight-line, between the approximate centres of each delivery area.
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Frequently asked questions
Where is ZIP code 51101?
ZIP code 51101 is in Sioux City, Iowa, in Woodbury County. ZIP codes are mail delivery routes rather than mapped regions, so the code identifies a set of addresses the Postal Service serves together, not a district with fixed borders.
What county is 51101 in?
51101 is in Woodbury County, Iowa. A single ZIP code can straddle a county line, because mail routes were drawn for delivery efficiency and take no notice of county boundaries, so the county shown is the one the code is primarily associated with.
What area code goes with ZIP code 51101?
ZIP codes and telephone area codes are separate systems with different boundaries, so no ZIP code maps to exactly one area code. Iowa uses 5 geographic area codes: 319, 515, 563, 641 and 712.
How many ZIP codes does Sioux City have?
Sioux City, Iowa has 9 ZIP codes in this dataset, of which 51101 is one. Large cities are split across many codes so mail can be sorted by district, and the codes are usually numerically close to each other.
Is 51101 a real ZIP code?
Yes. 51101 appears in the GeoNames postal-code dataset as an active US code assigned to Sioux City, Iowa. Codes that have been retired or never issued do not appear, which is why entering one on this site returns a not-found page rather than a blank record.
Why do ZIP code boundaries look odd on maps?
Because they are not boundaries. A ZIP code is a collection of mail routes, and a route is a line a carrier walks or drives, not an area. Any ZIP code map you have seen is somebody's approximation drawn around the addresses in a code, which is also why two ZIP code maps rarely agree with each other.
Can two addresses in the same ZIP code be in different cities?
Yes, routinely. The Postal Service assigns a preferred city name to each code for addressing purposes, and that name often covers several neighbouring towns, unincorporated areas or a whole postal district. The place shown here is the one the source names for the code, not a claim that every address in it is inside that town's limits.
ZIP code, place, county and location data from GeoNames, used under CC BY 4.0, extracted 2026-08-22. ZIP codes are Postal Service delivery routes, not administrative areas, so a code can cross city and county lines and the place name shown is the one the source records for the code. Coordinates are an approximate centre of the delivery area, not a precise location. Population and time zone are not shown because the source does not publish them.