| ZIP Codes: | 27 ZIP Codes (18 Standard, 8 PO Box, 1 Unique) [See All] |
| Area Codes: | 254 / 512 / 737 |
| Timezone: | Central (GMT -06:00) |
| Local Time: | 2:14:04 PM |
| Population: | 691,052 [See All] |
| FIPS: | 48491 |
| CBSA: | Austin-Round Rock-San Marcos, TX |
| Land Area: | 1,175 sq mi |
| Water Area: | 17 sq mi |
| Coordinates: | 30.6026, -97.6580 |
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691,052 residents live across 27 ZIPs covering 1,175 sq mi, served by 16 distinct USPS-recognized cities.
Population moved from 467,616 to 690,944 from 2014 to 2024 — a +47.8% change. 17 ZIPs gained residents, 2 lost.
The county's wealthiest ZIP 78717 (Austin, $145,325 median) and poorest ZIP 76574 (Taylor, $78,568) are 22.0 miles apart — a 1.8× income gap across local geography.
Median home values vary 2.3× across this county — from $288,300 in 76530 (Granger) to $652,200 in 78717 (Austin).
Density varies 140× across the county — from 27 people/sq mi in 76578 (Thrall) to 3,741 in 78664 (Round Rock).
Educational attainment ranges from 21.9% bachelor's+ in 76527 (Florence) to 68.9% in 78717 (Austin) — the breadth of educational profiles across the area.
Within Texas, this is the #11 most populous of 254 counties and ranks #10 for median household income with the #6 fastest decade growth .
On the national stage, Williamson County is the #100 most populous US county , and #16 for decade growth .
Hosts 1 single-entity Unique ZIP: 78682Dell Computers .
Weighted by population, the typical household earns about $117,747 across the county — reflecting what a typical resident sees, not a simple ZIP average.
49.2% of adults age 25+ hold a bachelor's degree or higher (231,549 of 470,820 reporting). The most-educated ZIPs cluster around Austin.
18 Standard delivery, 8 PO Box only, 1 single-entity Unique ZIPs serve this county.
2 ZIPs in this county where more than 60% of adults 25+ hold a bachelor's degree — typically college campuses, research enclaves, or tech corridors.
Williamson County grew 47.8% over the past decade — concentrated in 5 high-growth ZIPs:
| ZIP | City | Type | Population | Median Income | Area (sq mi) | 10-yr Growth |
|---|---|---|---|---|---|---|
| 78641 | Leander | Standard | 99,865 | $135,024 | 118.1 | 94.9% |
| 78613 | Cedar Park | Standard | 89,956 | $125,487 | 28.1 | 27.1% |
| 78665 | Round Rock | Standard | 66,171 | $122,680 | 23.6 | 70.4% |
| 78664 | Round Rock | Standard | 62,060 | $87,417 | 16.6 | 5.3% |
| 78681 | Round Rock | Standard | 56,691 | $137,819 | 24.7 | 4.0% |
| 78628 | Georgetown | Standard | 50,822 | $125,635 | 62.7 | 104.5% |
| 78626 | Georgetown | Standard | 48,072 | $100,431 | 90.4 | 71.1% |
| 78634 | Hutto | Standard | 46,413 | $114,426 | 57.1 | 82.6% |
| 78717 | Austin | Standard | 37,262 | $145,325 | 11.1 | 46.5% |
| 78729 | Austin | Standard | 30,460 | $86,438 | 10.0 | 5.8% |
| 78633 | Georgetown | Standard | 29,309 | $100,936 | 77.8 | 49.6% |
| 78642 | Liberty Hill | Standard | 26,434 | $132,958 | 110.7 | 167.9% |
| 76574 | Taylor | Standard | 20,242 | $78,568 | 153.2 | 11.6% |
| 76537 | Jarrell | Standard | 16,272 | $98,199 | 58.1 | 313.1% |
| 76527 | Florence | Standard | 4,918 | $81,574 | 120.8 | 18.4% |
| 76530 | Granger | Standard | 2,598 | $106,250 | 94.0 | -1.8% |
| 76578 | Thrall | Standard | 1,762 | $105,063 | 65.8 | 27.6% |
| 78615 | Coupland | Standard | 1,637 | $80,938 | 52.0 | 68.8% |
| 78674 | Weir | PO Box | 108 | — | 0.0 | — |
| 76573 | Schwertner | PO Box | 0 | — | 0.0 | -100.0% |
| 78673 | Walburg | PO Box | — | — | 0.0 | — |
| 78682 | Round Rock | Unique | — | — | 0.0 | — |
| 78683 | Round Rock | PO Box | — | — | 0.0 | — |
| 78680 | Round Rock | PO Box | — | — | 0.0 | — |
| 78630 | Cedar Park | PO Box | — | — | 0.0 | — |
| 78627 | Georgetown | PO Box | — | — | 0.0 | — |
| 78646 | Leander | PO Box | — | — | 0.0 | — |