The City of Aspen is the Home Rule Municipality that is the county seat and the most populous municipality of Pitkin County, Colorado, United States. The city population was 6,658 at the 2010 United States Census. Aspen is situated in a remote area of the Rocky Mountains' Sawatch Range and Elk Mountains, along the Roaring Fork River at an elevation just below above sea level on the Western Slope, west of the Continental Divide.