Hartsel is an unincorporated community with a U.S. Post Office located in Park County, Colorado, United States. Founded in 1880, Hartsel is at the geographic center of the state, it is often referred to as "The Heart of Colorado". The namesake of the community is Samuel Hartsel, a local cattle rancher who came to Park County in 1860 and left in 1908. He also raised pigs and sheep and grew on fifteen thousand acres oats, wheat, barley, rye, and hay.