Explore Union City local geography, civic resources and voter guides, with dated official population and registration facts for Alameda County.
At a glance: Union City is an incorporated city in Alameda County. Population: 66,665 (California Department of Finance estimate as of January 1, 2026). Registered voters: 41,710 (California Secretary of State, as of September 4, 2026).
Union City crosses the southern East Bay plain between Hayward and Fremont, with the older communities of Alvarado and Decoto forming distinct historical centers. Its western edge approaches the baylands, while eastern neighborhoods sit closer to the foothills. Kennedy Youth Center on Decoto Road provides teen-oriented space for computers, games, art, dance, and informal gathering. Its programs show how municipal community facilities serve needs beyond sports fields and general-purpose meeting rooms. Union City incorporated on January 13, 1959, joining Alvarado and Decoto in one municipality. It is a general-law city with council-manager government.
Alvarado and Decoto formed the incorporated municipality.
It is at 1333 Decoto Road.
The city lists a computer lab, game room, art and dance space, and indoor and outdoor teen lounge areas.
The Alameda County Registrar of Voters handles registration, ballots, and voting-location information.
41,710 (California Secretary of State, as of September 4, 2026).
CA Slates began with shared voter guides in 2012 and expanded into its current publication family and connected program.