Brentwood, CA has a population of 56,923 and is the 699th largest city in the United States. The population density is 3,831 per sq mi which is 1548% higher than the California average and 4128% higher than the national average. The median age in Brentwood is 38 which is approximately 6% higher than the California average of 36. In Brentwood, 63% of the population over 15 years of age are married, 77% speak English and 14% speak Spanish. 67% of Brentwood residents were born in California, 16% were born out of state, 1% were born outside of the United States and 16% were foreign born.