Castroville, CA has a population of 6,978 and is the 5,189th largest city in the United States. The population density is 6,830 per sq mi which is 2839% higher than the California average and 7438% higher than the national average. The median age in Castroville is 28 which is approximately 21% lower than the California average of 36. In Castroville, 53% of the population over 15 years of age are married, 16% speak English and 76% speak Spanish. 52% of Castroville residents were born in California, 3% were born out of state, 1% were born outside of the United States and 44% were foreign born.