Clackamas County (/ˈklækəməs/ CLAK-ə-məss) 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 Native Americans living in the area, the Clackamas people, who are part of the Chinookan peoples.