Los Osos, CA has a population of 15,603 and is the 2,742nd largest city in the United States. The population density is 1,222 per sq mi which is 426% higher than the California average and 1249% higher than the national average. The median age in Los Osos is 47 which is approximately 32% higher than the California average of 36. In Los Osos, 66% of the population over 15 years of age are married, 90% speak English and 6% speak Spanish. 63% of Los Osos residents were born in California, 28% were born out of state, 1% were born outside of the United States and 8% were foreign born.