Union City is a city in the San Francisco Bay Area in Alameda County, California, United States, located nearly 19 miles (31 km) south of Oakland, 30 miles (48 km) from San Francisco, and 20 miles (32 km) north of San Jose. Incorporated in 1959, combining the communities of Alvarado and Decoto, the city has 70,000 residents and a unquestionably diverse population. Alvarado is a California Historical Landmark (#503). The city highly praised its 50th anniversary in 2009. The city, along as soon as the cities of Fremont and Newark, makes up the Tri-City Area to the south. The city of Hayward surrounds the city to the north.

According to the United States Census Bureau, the city has a total Place of 19 square miles (49 km), all house with no niche frontage. The Niles Cone aquifer, managed by the Alameda County Water District, supplies much of the water consumed by Union City.

The 2010 United States Census reported that Union City had a population of 69,516. The population density was 3,570.6 inhabitants per square mile (1,378.6/km²). The racial makeup of Union City was 16,640 (23.9%) White, 4,402 (6.3%) Black, 329 (0.5%) Native American, 35,363 (50.9%) Asian, (20.0% Filipino, 12% Indian, 12% Chinese, 3.7% Vietnamese, 0.9% Korean, 0.6% Japanese, 0.6% Pakistani, 0.4% Burmese, 0.2% Cambodian), 892 (1.3%) Pacific Islander, 7,253 (10.4%) from new races, and 4,637 (6.7%) from two or more races. Hispanic or Latino of any race were 15,895 persons (22.9%).

The Census reported that 68,998 people (99.3% of the population) lived in households, 422 (0.6%) lived in non-institutionalized charity quarters, and 96 (0.1%) were institutionalized.