 Fort Collins is the fourth most populous city in Colorado and the 158th most populous city in the United States.The Census Bureau estimates that the city's population was 161,175 in 2015, the population of the Fort Collins-Loveland Metropolitan Statistical Area was 310,487 (151st most populous MSA), and the population of the Front Range Urban Corridor was 4,495,181.As of the census of 2000, there were 118,652 people, 45,882 households, and 25,785 families residing in the city.