Mount Rainier National Park is an American national park located in southeast Pierce County and northeast Lewis County in Washington state. The park was established on March 2, 1899, as the fourth national park in the United States, preserving 236,381 acres including all of Mount Rainier, a 14,410-foot (4,390 m) stratovolcano. The mountain rises abruptly from the surrounding land with elevations in the park ranging from 1,600 feet to over 14,000 feet (490–4,300 m). The highest point in the Cascade Range, Mount Rainier is surrounded by valleys, waterfalls, subalpine meadows, and 91,000 acres of old-growth forest. More than 25 glaciers descend the flanks of the volcano, which is often shrouded in clouds that dump enormous amounts of rain and snow.

Pierce County is a county in the U.S. state of Washington. As of the 2020 census, the population was 921,130, up from 795,225 in 2010, making it the second-most populous county in Washington, behind King County, and the 59th-most populous in the United States. The county seat and largest city is Tacoma. Formed out of Thurston County on December 22, 1852, by the legislature of Oregon Territory, it was named for U.S. President Franklin Pierce. Pierce County is in the Seattle metropolitan area.