Union City - Hardcoverby Timothy Swenson (Author) Union City was formed by the merging of two communities, Alvarado and Decoto. In the early 1850s, Alvarado was founded as a place to ship local produce to San Francisco. When Alameda County was created in 1853, Alvarado became the county seat and the hub of business activity for the county. The proximity of Alameda Creek to Alvarado, with its yearly floods, would cause the county seat to move to San Leandro and then