Costanoans ("coastal peoples") were the first inhabitants, primarily the Ohlone peoples living alongside the
Alameda and Dry Creeks. Shell mounds along the sloughs of Alameda Creek near the Alvarado sugar mill contained burial sites. The first non-native community was founded in 1850 by John and William Horner, who named it "Union City" after their
Sacramento River Steamship, "The Union". In 1854, it merged with the nearby community of New Haven (founded 1851) to form the town of
Alvarado, named after a former Mexican governor,
Juan Bautista Alvarado. Alvarado was the first
county seat of
Alameda County, a designation it lost in 1865 to
San Leandro. Further east,
Decoto was founded in 1870 as a railroad hub, hosting the
first transcontinental railroad. Union City is a former railroad and steel town with an extensive industrial heritage. The Pacific States Steel Company occupied the land behind Union City Station that is redeveloping into the Union City Station District Downtown. The Alvarado and Decoto neighborhoods were both former railroad hubs and active railroad lines bisect both East End and the West Side of town. Trains are a way of life in Union City and natives are accustomed to waiting for Amtrak and freight trains to cross while commuting. In the 1950s, Alvarado and Decoto – the latter making up the eastern side of the town – were annexation targets of the nearby communities of Newark, Hayward, and what would become Fremont. On January 13, 1959, they decided to incorporate into a single city, and named it after the Horners' original settlement, Union City. Tom Kitayama served as the city's first mayor in 1959 and was involved in Union City politics until his 1991 retirement. In March 2025, the city of Union City rolled out new city branded color coded trash carts with Republic Services and local Tri-CED community recycling to meet state and local goals. ==Economy==