Mount Rainier National Park is a United States National Park located in southeast Pierce County and northeast Lewis County in Washington state. It was established on March 2, 1899 as the fifth national park in the United States. The park encompasses 236,381 acres (369.35 sq mi; 956.60 km2) including all of Mount Rainier, a 14,410-foot (4,390 m) stratovolcano.