South San Francisco, CA has a population of 66,587 and is the 561st largest city in the United States. The population density is 7,255 per sq mi which is 3022% higher than the California average and 7908% higher than the national average. The median age in South San Francisco is 39 which is approximately 8% higher than the California average of 36. In South San Francisco, 57% of the population over 15 years of age are married, 43% speak English and 25% speak Spanish. 52% of South San Francisco residents were born in California, 6% were born out of state, 2% were born outside of the United States and 40% were foreign born.