Johnstown is a home rule municipality in Weld and Larimer counties in the U.S. state of Colorado. The population was 17,303 at the 2020 United States Census.

Larimer County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 359,066. The county seat and most populous city is Fort Collins. The county was named for William Larimer, Jr., the founder of Denver.