Columbus is a consolidated city-county located on the west-central border of the U.S. state of Georgia. Columbus lies on the Chattahoochee River directly across from Phenix City, Alabama. It is the county seat of Muscogee County, with which it officially merged in 1970. Columbus is the second-largest city in Georgia (after Atlanta), and fields the state's fourth-largest metropolitan area. According to the 2020 census from the U.S. Census Bureau, Columbus has a population of 206,922 residents, with 328,883 in the Columbus metropolitan area. The metro area joins the nearby Alabama cities of Auburn and Opelika to form the Columbus–Auburn–Opelika Combined Statistical Area, which has an estimated population of 486,645 in 2019, according to the U.S. Census Bureau.Columbus lies 100 miles (160 km) southwest of Atlanta. Fort Benning, the United States Army's Maneuver Center of Excellence and a major employer, is located south of the city in southern Muscogee and Chattahoochee counties. Columbus is home to museums and tourism sites, including the National Infantry Museum, dedicated to the U.S. Army's Infantry Branch. It has the longest urban whitewater rafting course in the world constructed on the Chattahoochee River.