Simi Valley, CA has a population of 126,126 and is the 221st largest city in the United States. The population density is 3,041 per sq mi which is 1209% higher than the California average and 3256% higher than the national average. The median age in Simi Valley is 40 which is approximately 11% higher than the California average of 36. In Simi Valley, 59% of the population over 15 years of age are married, 74% speak English and 15% speak Spanish. 61% of Simi Valley residents were born in California, 19% were born out of state, 1% were born outside of the United States and 19% were foreign born.