Portland is the largest city in the U.S. state of Oregon and the seat of Multnomah County. It is located in the Willamette Valley region of the Pacific Northwest, at the confluence of the Willamette and Columbia rivers. The city covers 145 square miles and had an estimated population of 632,309 in 2015, making it the 26th most populous city in the United States. Approximately 2,389,228 people live in the Portland metropolitan statistical area (MSA), the 23rd most populous MSA in the United States. Its Combined Statistical Area (CSA) ranks 17th with a population of 3,022,178. Roughly 60 percent of Oregon's population resides within the Portland metropolitan area.