Johnstown, CO has a population of 14,379 and is the 2,928th largest city in the United States. The population density is 1,052 per sq mi which is 2012% higher than the Colorado average and 1061% higher than the national average. The median age in Johnstown is 34 which is approximately 7% lower than the Colorado average of 36. In Johnstown, 74% of the population over 15 years of age are married, 88% speak English and 10% speak Spanish. 52% of Johnstown residents were born in Colorado, 41% were born out of state, 0% were born outside of the United States and 6% were foreign born.