There are 7 US Post Offices in Polk County serving a total of 73,748 residents equating to 10,535 residents per post office. It's estimated that approximately 117,710 packages are handled across the 7 county post offices annually. Polk County is a county located in the U.S. state of Oregon. As of the 2010 census, the population was 75,403. 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."