Hillsborough, CA has a population of 11,312 and is the 3,581st largest city in the United States. The population density is 1,827 per sq mi which is 614% higher than the California average and 1917% higher than the national average. The median age in Hillsborough is 47 which is approximately 31% higher than the California average of 36. In Hillsborough, 75% of the population over 15 years of age are married, 72% speak English and 4% speak Spanish. 49% of Hillsborough residents were born in California, 26% were born out of state, 2% were born outside of the United States and 23% were foreign born.