San Marino, CA has a population of 13,324 and is the 3,134th largest city in the United States. The population density is 3,537 per sq mi which is 1422% higher than the California average and 3804% higher than the national average. The median age in San Marino is 47 which is approximately 30% higher than the California average of 36. In San Marino, 72% of the population over 15 years of age are married, 44% speak English and 8% speak Spanish. 44% of San Marino residents were born in California, 14% were born out of state, 2% were born outside of the United States and 40% were foreign born.