Welby, CO has a population of 16,771 and is the 2,550th largest city in the United States. The population density is 4,538 per sq mi which is 9014% higher than the Colorado average and 4909% higher than the national average. The median age in Welby is 30 which is approximately 18% lower than the Colorado average of 36. In Welby, 45% of the population over 15 years of age are married, 59% speak English and 37% speak Spanish. 55% of Welby residents were born in Colorado, 23% were born out of state, 1% were born outside of the United States and 21% were foreign born.