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ZIP codes in Boulder County

30 ZIPs touch Boulder County, Colorado. The blue dashed line is the county border; orange ZIPs reach into it.

30

ZIP codes

8

cross the county line

481,489

people in these ZIPs

64

counties in CO

Most people

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Boulder County ZIP list

More counties in Colorado

All 64 counties in Colorado

Questions people actually ask

How many ZIP codes are in Boulder County, Colorado?

30 ZIP codes reach into Boulder County, including 7 PO Box or single-address ZIPs placed by the town they serve. 8 of them are only partly in the county and also cover a neighboring county.

Which ZIP code in Boulder County has the most people?

80504 (Longmont) has about 63,451 residents, the most of any ZIP touching Boulder County, in the Census Bureau’s ACS 2020–2024 estimates.

Can a ZIP code be in Boulder 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 Boulder 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