Pitkin County is a county in the U.S. state of Colorado. As of the 2020 census, the population was 17,358. The county seat and largest city is Aspen. The county is named for Colorado Governor Frederick Walker Pitkin.

Aspen is a home rule municipality that is the county seat and the most populous municipality of Pitkin County, Colorado, United States. The city population was 7,004 at the 2020 United States Census. Aspen is in a remote area of the Rocky Mountains' Sawatch Range and Elk Mountains, along the Roaring Fork River at an elevation just below 8,000 feet (2,400 m) above sea level on the Western Slope, 11 miles (18 km) west of the Continental Divide. Aspen is now a part of the Glenwood Springs, CO Micropolitan Statistical Area.