Clackamas County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 421,401, making it Oregon's third-most populous county. Its county seat is Oregon City. The county was named after the American Indians living in the area, the Clackamas people, who are part of the Chinookan peoples. Clackamas County is part of the Portland-Vancouver-Hillsboro, OR-WA Metropolitan Statistical Area. It is in the Willamette Valley.