St. Louis is an independent city in Missouri. It is the largest metropolitan area in the state of Missouri; however, the independent city of St. Louis is the second largest city in Missouri, behind Kansas City. It is situated along the western bank of the Mississippi River, which forms the state line between Illinois and Missouri. The Missouri River merges with the Mississippi River 15 river miles north of Downtown St. Louis, forming the fourth longest river system in the world. The estimated 2018 population of the city proper was 302,838 and the bi-state metropolitan area was 2,804,724. Greater St. Louis is the largest metropolitan area in Missouri, second-largest in Illinois, seventh-largest in the Great Lakes Megalopolis, and the 20th-largest in the United States.