Frederick, CO has a population of 10,791 and is the 3,722nd largest city in the United States. The population density is 763 per sq mi which is 1433% higher than the Colorado average and 742% higher than the national average. The median age in Frederick is 35 which is approximately 3% lower than the Colorado average of 36. In Frederick, 70% of the population over 15 years of age are married, 94% speak English and 4% speak Spanish. 48% of Frederick residents were born in Colorado, 47% were born out of state, 1% were born outside of the United States and 4% were foreign born.