Alameda County has announced an agreement with the US Postal Service (USPS) to let the unincorporated communities of Ashland, Castro Valley, Cherryland, Fairview and Hayward Acres and San Lorenzo be recognized by their community's place name as the default "city" in mailing addresses. When Zip Codes were established in the 1960s, unincorporated areas were assigned place names of neighboring incorporated cities. As convenient as that convention may have been for the USPS, Zip Codes can mislead the public about community identity. That problem became further complicated as computing technology evolved. For example, algorithms that drive online shopping would reject unincorporated area's place names if shoppers who lived in unincorporated communities dared to enter the names of where they lived in their shipping address instead of the name of the adjacent city. More dire complications can occur because Zip Codes have become handy for the collection and reporting of demographic data that are used to drive public policy and funding decisions - impacting representation in Congress, the Legislature and local public entities along with significant amounts of public spending

Some unincorporated communities do not share Zip Codes with nearby or adjacent cities. Among others, unincorporated Carmichael, Fair Oaks, Orangevale and Rio Linda in Sacramento County are associated by their USPS Zip Codes and they have USPS branches that bear the name of the local unincorporated community. Still other Zip Codes - like Arden Acade and Vineyard - though they serve hundreds of thousands of Sacramento County's unincorporated area postal addresses, stipulate that the official place name of the community is "Sacramento", whether or not the Zip Code's postal addresses are in the City of Sacramento. One result has been the County's habit of listing the unincorporated communities' voting locations as being within the City of Sacramento, a practice that has confused voters.

The City of Menifee, in Riverside County, incorporated in 2008, unified several unincorporated places within its boundaries. In 2009, the City asked the USPS Postmaster to use Menifee as the preferred place name for all mailing addresses within the city. The approval process took years until local citizens circulated a petition in late 2017. Not long afterwards, the City Council resolved (1/17/18 agenda item 12.3) that the USPS default place name should be "Menifee" for all the city's residents.

In Alameda County, some Zip Codes in both Castro Valley and San Lorenzo have USPS branches that have historically been identified by the name of their communty. But there are parts of Castro Valley and San Lorenzo with Zip Codes that have historically been identified as being part of the cities of San Leandro or Hayward. After a over 10 years of advocacy by the Eden Area Livibility Initiative the County has determined that the Zip Codes for all of the unincorporated communities studied should use the default names to those of the unincorporated communities. The County has begun an outreach campaign to inform the public about the changes.