Pierce County is a county in the U.S. state of Washington. As of the 2010 Census, the population was 795,225, making it the second-most populous county in Washington behind King County. The county seat and largest city is Tacoma. Pierce County is included in the Seattle-Tacoma-Bellevue, WA Metropolitan Statistical Area. Pierce County is notable for being home to Mount Rainier, the tallest mountain and a volcano in the Cascade Range. Pierce County was created from Thurston County by the legislature of Oregon Territory on December 22, 1852, and was named for U.S. President Franklin Pierce. Pierce County is home to Joint Base Lewis-McChord, the largest joint base on the West Coast of the United States and the third-largest in the U.S. Department of Defense.