Union City, CA ZIP Codes
Union City, California has 2 ZIP codes: 2 for street addresses ( and ).
Your street decides which one you use.
Which Union City ZIP code is my address in?
Street ranges from the Census Bureau, 2026. PO box and organization ZIP codes are not found by street. A new street may be missing: address not found?
Union City ZIP code map
Tap or point to an area to see its ZIP code.Full-size map
Dashed line: Union City city limits.
Map: Census Bureau ZIP Code Tabulation Areas (2020) and place limits (2024).
All Union City ZIP codes by type
| ZIP | Type and post office or station |
|---|---|
| 94552 | street delivery; mail may be addressed to Castro Valley Castro Valley |
| 94587 | street delivery Alvarado |
Why your mail may say Union City when you live outside it
Union City ZIP codes also cover Castro Valley, so a letter addressed to Union City can go to a home outside the city limits.
A ZIP code does not set your city, school district or tax. Alameda County property records show which city you are in.
Union City ZIP code questions
What is the main ZIP code for Union City?
94552, the ZIP code of the main Castro Valley post office at 20283 Santa Maria Ave.
What county is Union City in?
Alameda County.
ZIP codes for towns near Union City
More towns near Union City: San Leandro, Menlo Park, Redwood City, San Ramon, Foster City, Milpitas, Mountain View, Danville, Sunnyvale.
Sources and last checked
USPS ZIP Locale Detail (October 1, 2026), GeoNames (CC BY 4.0), U.S. Census Bureau, HUD-USPS crosswalk.
Checked October 20, 2026. Sources · How we build our lists · Corrections