St. Louis (/seɪnt ˈluːɪs/ or /sənt ˈluːɪs/) is a city and port in the U.S. state of Missouri. The city developed along the western bank of the Mississippi River, which forms Missouri's border with Illinois. In 2010, St. Louis had a population of 319,294; a 2013 estimate put the population at 318,416, making it the 58th-most populous U.S. city and the second-largest city in the state in terms of city proper population, second only to Kansas City. The St.