Tulsa (pronounce /ˈtʌlsə/) is the second-largest city in the state of Oklahoma and 45th-largest in the United States. With an estimated population of 382,872 in 2006, it is the principal municipality of the Tulsa Metropolitan Statistical Area, a region of 905,755 residents projected to reach one million between 2010 and 2012. In 2007, the Tulsa-Bartlesville Combined Statistical Area had a population of 955,643 residents. The city serves as the county seat of Tulsa County, the most densely populated county in Oklahoma, and extends into Osage, Rogers, and Wagoner counties.