Millbrae, CA has a population of 22,522 and is the 1,930th largest city in the United States. The population density is 6,927 per sq mi which is 2881% higher than the California average and 7546% higher than the national average. The median age in Millbrae is 44 which is approximately 23% higher than the California average of 36. In Millbrae, 63% of the population over 15 years of age are married, 50% speak English and 8% speak Spanish. 49% of Millbrae residents were born in California, 10% were born out of state, 2% were born outside of the United States and 38% were foreign born.