There are 6 US Post Offices in Cook County serving a total of 5,176 residents equating to 863 residents per post office. It's estimated that approximately 8,261 packages are handled across the 6 county post offices annually. Not to be confused with Cook, Minnesota in Saint Louis County. Cook County is a county located in the U.S. state of Minnesota. As of the 2010 census, the population was 5,176, making it the fifth-least populous county in Minnesota. Its county seat is Grand Marais. The Grand Portage Indian Reservation is entirely within the county."