San Luis Obispo, CA has a population of 46,716 and is the 885th largest city in the United States. The population density is 3,557 per sq mi which is 1430% higher than the California average and 3826% higher than the national average. The median age in San Luis Obispo is 26 which is approximately 28% lower than the California average of 36. In San Luis Obispo, 35% of the population over 15 years of age are married, 83% speak English and 12% speak Spanish. 67% of San Luis Obispo residents were born in California, 22% were born out of state, 1% were born outside of the United States and 9% were foreign born.