St. Louis () is a major 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 2018 population of 302,838 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, and the 20th-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. In 1764, following France's defeat in the Seven Years' War, the area was ceded to Spain and retroceded back to France in 1800. In 1803, the United States acquired the territory as part of the Louisiana Purchase. During the 19th century, St. Louis became a major port on the Mississippi River; at the time of the 1870 Census, it was the fourth-largest city in the country.