There are 14 US Post Offices in Polk County serving a total of 31,068 residents equating to 2,219 residents per post office. It's estimated that approximately 49,588 packages are handled across the 14 county post offices annually. Polk County is a county located in the U.S. state of Minnesota. The population was 31,600 at the 2010 census. Its county seat is Crookston, and the largest community is East Grand Forks. Polk County is included in the Grand Forks, ND-MN Metropolitan Statistical Area."