County ZIP codes · Texas · FIPS 48491
Williamson County, TX ZIP Codes
Williamson County, Texas has 34 ZIP codes (Census 2020 ZCTA-county file; GeoNames postal codes, October 2026): 27 residential and 7 for PO boxes or a single organization. 19 of the residential ones lie mainly in Williamson County and 8 mainly in a neighboring county; 14 cross the county line. Median household income ranges from $69,286 in 76511 (Bartlett) to $145,325 in 78717 (Austin) (Census Bureau, ACS 2020-2024).
- ACS2020-24
- Census2020
Where are the ZIP codes of Williamson County?
Source: U.S. Census Bureau, 2020 ZCTA cartographic boundaries; ACS 2020-2024 5-year estimates (B19013).
How different are its ZIP codes?
The middle half of its ranked ZIP codes (1,000+ people living in households) report median household incomes between $87,417 and $122,680.
They carry 18 postal town names.
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates (B19013).
All 27 residential ZIP codes in Williamson County
19 ZIP codes lie mainly in Williamson County; 8 more reach into it from a neighboring county and follow the first table.
| In this county | ||||||
|---|---|---|---|---|---|---|
| 78613 | Cedar Park | 89,956 | 3,248 | $126k | $496k | 89% |
| 78665 | Round Rock | 66,171 | 2,748 | $123k | $474k | 100% |
| 78664 | Round Rock | 62,060 | 3,736 | $87k | $358k | 86% |
| 78681 | Round Rock | 56,691 | 2,445 | $138k | $497k | 100% |
| 78628 | Georgetown | 50,822 | 785 | $126k | $497k | 100% |
| 78626 | Georgetown | 48,072 | 543 | $100k | $388k | 100% |
| 78634 | Hutto | 46,413 | 823 | $114k | $375k | 100% |
| 78717 | Austin | 37,262 | 2,856 | $145k | $652k | 100% |
| 78729 | Austin | 30,460 | 3,104 | $86k | $476k | 88% |
| 78633 | Georgetown | 29,309 | 374 | $101k | $465k | 100% |
| 78642 | Liberty Hill | 26,434 | 238 | $133k | $507k | 92% |
| 76574 | Taylor | 20,242 | 136 | $79k | $298k | 100% |
| 76537 | Jarrell | 16,272 | 303 | $98k | $291k | 100% |
| 76527 | Florence | 4,918 | 41 | $82k | $345k | 86% |
| 76530 | Granger | 2,598 | 28 | $106k | $288k | 100% |
| 76578 | Thrall | 1,762 | 27 | $105k | $341k | 99% |
| 78615 | Coupland | 1,637 | 30 | $81k | $441k | 64% |
| 78674 | Weir | 108 | 302 | – | $48k | 100% |
| 76573 | Schwertner | no residents | 0 | – | – | 100% |
Partly in Williamson County
| In this county | ||||||
|---|---|---|---|---|---|---|
| 78641 | Leander | 99,865 | 803 | $135k | $480k | 37% |
| 76511 | Bartlett | 2,702 | 33 | $69k | $223k | 37% |
| 78750 | Austin | 29,277 | 2,482 | $122k | $602k | 22% |
| 78728 | Austin | 26,777 | 3,456 | $75k | $437k | 22% |
| 78621 | Elgin | 30,411 | 171 | $99k | $321k | 14% |
| 76577 | Thorndale | 3,128 | 22 | $64k | $218k | 10% |
| 78727 | Austin | 29,958 | 3,856 | $110k | $540k | 2% |
| 78759 | Austin | 43,182 | 3,030 | $102k | $674k | 1% |
Source: U.S. Census Bureau, ACS 2020-2024 5-year estimates; county shares by land area (Census 2020 ZCTA-county relationship file).
Which ZIP codes cross the county line?
15 ZIP codes of Williamson County extend into another county. A ZIP code follows mail routes, not county borders.
| ZIP | In Williamson | Elsewhere |
|---|---|---|
| 78641 | 37% | Travis County 63% |
| 78613 | 89% | Travis County 11% |
| 78664 | 86% | Travis County 14% |
| 78759 | 1% | Travis County 99% |
| 78729 | 88% | Travis County 12% |
| 78621 | 14% | Bastrop County 63%; Travis County 15%; Lee County 9% |
| 78727 | 2% | Travis County 98% |
| 78750 | 22% | Travis County 78% |
| 78728 | 22% | Travis County 78% |
| 78642 | 92% | Burnet County 8% |
| 76527 | 86% | Burnet County 8%; Bell County 7% |
| 76577 | 10% | Milam County 90% |
| 76511 | 37% | Bell County 57%; Milam County 6% |
| 76578 | 99% | |
| 78615 | 64% | Travis County 36% |
Source: U.S. Census Bureau, 2020 ZCTA-county relationship file (shares of land area).
PO Box and single-organization ZIP codes
Source: GeoNames postal codes (CC BY 4.0).
Which first three digits do Williamson County's ZIP codes use?
The first three digits of a ZIP code name the sectional center, the mail processing plant that sorts it. Williamson County's ZIP codes use 3 prefixes: 765, 786 and 787.
| Prefix | Sectional center | Here | All codes |
|---|---|---|---|
| 765 | Austin, TX (SCF 786) | 8 | 55 |
| 786 | Austin, TX (SCF 786) | 20 | 75 |
| 787 | Austin, TX (SCF 786) | 6 | 72 |
Source: U.S. Postal Service, labeling list L005 (3-digit ZIP Code prefix groups, SCF sortation), effective October 1, 2026.