Grass Valley, CA has a population of 12,861 and is the 3,233rd largest city in the United States. The population density is 2,450 per sq mi which is 954% higher than the California average and 2604% higher than the national average. The median age in Grass Valley is 48 which is approximately 32% higher than the California average of 36. In Grass Valley, 49% of the population over 15 years of age are married, 90% speak English and 7% speak Spanish. 64% of Grass Valley residents were born in California, 27% were born out of state, 1% were born outside of the United States and 8% were foreign born.