San Anselmo, CA has a population of 12,623 and is the 3,285th largest city in the United States. The population density is 4,715 per sq mi which is 1929% higher than the California average and 5104% higher than the national average. The median age in San Anselmo is 47 which is approximately 30% higher than the California average of 36. In San Anselmo, 65% of the population over 15 years of age are married, 90% speak English and 4% speak Spanish. 57% of San Anselmo residents were born in California, 34% were born out of state, 1% were born outside of the United States and 7% were foreign born.