St. Louis, Missouri, the second largest city in the state. It adjoins, but is independent of, St. Louis County. The city lies on the west bank of the Mississippi River, just south of the river's junction with the Missouri River. With its metropolitan area, which includes adjacent parts of Missouri and Illinois, St. Louis is a major center of transportation, manufacturing, commerce, and education.

Because of its historic role in the nation's westward expansion, St. Louis is frequently called “Gateway to the West.” The commemorative Gateway Arch, designed by Eero Saarinen, is the focal point of the Jefferson National Expansion Memorial on the downtown riverfront.