St. Louis (/seɪnt ˈluːɪs, sənt-/ saynt LOO-iss, sənt-, sometimes referred to as St. Louis City, Saint Louis or STL) is an independent city in the U.S. state of Missouri. It lies near the confluence of the Mississippi and the Missouri rivers. In 2020, the city proper had a population of 301,578, while its metropolitan area, which extends into Illinois, had an estimated population of over 2.8 million. It is the largest metropolitan area in Missouri and the second-largest in Illinois. The city's combined statistical area is the 20th-largest in the United States.
The land that became St. Louis had been occupied by Native American cultures for thousands of years before European settlement. The city was founded on February 14, 1764, by French fur traders Gilbert Antoine de St. Maxent, Pierre Laclède, and Auguste Chouteau. They named it for King Louis IX of France, and it quickly became the regional center of the French Illinois Country. In 1804, the United States acquired St. Louis as part of the Louisiana Purchase. In the 19th century, St. Louis developed as a major port on the Mississippi River; from 1870 until the 1920 census, it was the fourth-largest city in the country. It separated from St. Louis County in 1877, becoming an independent city and limiting its political boundaries. In 1904, it hosted the Louisiana Purchase Exposition, also known as the St. Louis World's Fair, and the Summer Olympics.