19 ZIP Codes
| Zip Code | City | Population ↓ |
|---|---|---|
| 78613 | Cedar Park | 89,956 |
| 78665 | Round Rock | 66,171 |
| 78664 | Round Rock | 62,060 |
| 78681 | Round Rock | 56,691 |
| 78628 | Georgetown | 50,822 |
| 78626 | Georgetown | 48,072 |
| 78634 | Hutto | 46,413 |
| 78717 | Austin | 37,262 |
| 78729 | Austin | 30,460 |
| 78633 | Georgetown | 29,309 |
| 78642 | Liberty Hill | 26,434 |
| 76574 | Taylor | 20,242 |
| 76537 | Jarrell | 16,272 |
| 76527 | Florence | 4,918 |
| 76530 | Granger | 2,598 |
| 76578 | Thrall | 1,762 |
| 78615 | Coupland | 1,637 |
| 78674 | Weir | 108 |
| 76573 | Schwertner | 0 |
The data shown reflect ZCTAs from the US Census. As of 2025, there are 19 ZCTAs in Williamson County, Texas (US Census).