ZIP Codes in Round Rock, TX
Round Rock uses 3 ZIP codes, all in Williamson County. Pick one below for details, or look up the full nine-digit ZIP+4 for a specific street address.
All 3 Round Rock ZIP codes
| ZIP | Type | County | Population |
|---|---|---|---|
| 78664 | standard | Williamson | 62,060 |
| 78665 | standard | Williamson | 66,171 |
| 78681 | standard | Williamson | 56,691 |
Finding a ZIP+4 in Round Rock
Knowing which of these 3 ZIP codes covers an address only gets you partway. The four-digit extension identifies the specific delivery point — typically one side of one block. Two houses facing each other on the same Round Rock street almost always have different ZIP+4 codes even though they share all five leading digits.
Appending ZIP+4 to a mailing list?
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