There are 2 US Post Offices in Bennett County serving a total of 3,151 residents equating to 1,576 residents per post office. It's estimated that approximately 5,029 packages are handled across the 2 county post offices annually. Bennett County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 3,431. Its county seat is Martin. The county was created in 1909 and organized in 1912. The northwestern section of the county lies within the Pine Ridge Indian Reservation. The North American continental pole of inaccessibility is in Bennett County, located 1650 km (1024 mi) from the nearest coastline, between Allen and Kyle (Oglala Lakota County) at 43.36\u00b0N 101.97\u00b0W\ufeff / 43.36; -101.97\ufeff (Pole of Inaccessibility North America)."