Clifton, CO has a population of 20,021 and is the 2,176th largest city in the United States. The population density is 3,304 per sq mi which is 6535% higher than the Colorado average and 3546% higher than the national average. The median age in Clifton is 33 which is approximately 10% lower than the Colorado average of 36. In Clifton, 53% of the population over 15 years of age are married, 91% speak English and 9% speak Spanish. 56% of Clifton residents were born in Colorado, 39% were born out of state, 1% were born outside of the United States and 4% were foreign born.