Fairfax, CA has a population of 7,598 and is the 4,881st largest city in the United States. The population density is 3,448 per sq mi which is 1384% higher than the California average and 3706% higher than the national average. The median age in Fairfax is 46 which is approximately 27% higher than the California average of 36. In Fairfax, 58% of the population over 15 years of age are married, 90% speak English and 4% speak Spanish. 54% of Fairfax residents were born in California, 35% were born out of state, 2% were born outside of the United States and 9% were foreign born.