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. Pitkin County has the seventh-highest per capita income of any U.S. county. Measured by mean income of the top 5% of earners, it is the wealthiest U.S. county.