Alum Rock, CA has a population of 11,877 and is the 3,443rd largest city in the United States. The population density is 13,995 per sq mi which is 5367% higher than the California average and 15347% higher than the national average. The median age in Alum Rock is 33 which is approximately 9% lower than the California average of 36. In Alum Rock, 53% of the population over 15 years of age are married, 35% speak English and 51% speak Spanish. 58% of Alum Rock residents were born in California, 5% were born out of state, 1% were born outside of the United States and 36% were foreign born.