Castro Valley, CA has a population of 62,825 and is the 600th largest city in the United States. The population density is 3,787 per sq mi which is 1530% higher than the California average and 4080% higher than the national average. The median age in Castro Valley is 42 which is approximately 16% higher than the California average of 36. In Castro Valley, 62% of the population over 15 years of age are married, 66% speak English and 10% speak Spanish. 59% of Castro Valley residents were born in California, 15% were born out of state, 1% were born outside of the United States and 25% were foreign born.