Hartsel is an unincorporated town and a U.S. Post Office located in Park County, Colorado, United States. Hartsel was founded in 1880. Located at the geographic center of the state, it is often referred to as "The Heart of Colorado". The community's namesake is Samuel Hartsel, a local cattle rancher. The Hartsel Post Office has the ZIP Code 80449. The ZCTA for 80449 had a population of 677 at the 2000 census.