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ZIP codes in Williamson County

33 ZIPs touch Williamson County, Texas. The blue dashed line is the county border; orange ZIPs reach into it.

33

ZIP codes

17

cross the county line

856,487

people in these ZIPs

254

counties in TX

Most people

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Williamson County ZIP list

More counties in Texas

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Questions people actually ask

How many ZIP codes are in Williamson County, Texas?

33 ZIP codes reach into Williamson County, including 6 PO Box or single-address ZIPs placed by the town they serve. 17 of them are only partly in the county and also cover a neighboring county.

Which ZIP code in Williamson County has the most people?

78641 (Leander) has about 99,865 residents, the most of any ZIP touching Williamson County, in the Census Bureau’s ACS 2020–2024 estimates.

Can a ZIP code be in Williamson 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 Williamson 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