St. Louis () is an independent city and inland port in the U.S. state of Missouri. It is situated along the western bank of the Mississippi River, which marks Missouri's border with Illinois. The Missouri River merges with the Mississippi River just north of the city. These two rivers combined form the fourth longest river system in the world. The city had an estimated 2017 population of 308,626 and is the cultural and economic center of the St. Louis metropolitan area (home to nearly 3,000,000 people), which is the largest metropolitan area in Missouri, the second-largest in Illinois (after Chicago), and the 22nd-largest in the United States.
Before European settlement, the area was a regional center of Native American Mississippian culture. The city of St. Louis was founded in 1764 by French fur traders Pierre Laclède and Auguste Chouteau, and named after Louis IX of France.