Union City, CA has a population of 73,500 and is the 485th largest city in the United States. The population density is 3,789 per sq mi which is 1530% higher than the California average and 4082% higher than the national average. The median age in Union City is 38 which is approximately 4% higher than the California average of 36. In Union City, 62% of the population over 15 years of age are married, 38% speak English and 14% speak Spanish. 45% of Union City residents were born in California, 9% were born out of state, 1% were born outside of the United States and 45% were foreign born.