NorthWestern Corporation, doing business as NorthWestern Energy, provides electricity and natural gas in Montana, South Dakota, and Nebraska, the United States. It operates through Electric Operations and Natural Gas Operations segments. The company generates, transmits, and distributes electricity, as well as purchases, transmits, distributes, and stores natural gas. As of February 27, 2013, it served approximately 673,200 residential, commercial, and industrial customers. The company was founded in 1923 and is based in Sioux Falls, South Dakota.