Polk County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 87,433. The county seat is Dallas. The county is named for James Knox Polk, the 11th president of the United States. Polk County is part of the Salem, OR Metropolitan Statistical Area, which is also included in the Portland-Vancouver-Salem, OR-WA Combined Statistical Area. It is located in the Willamette Valley.