Louisiana is a city in Pike County, Missouri, United States. The population was 3,364 at the 2010 census. Louisiana is located in northeast Missouri, on the Mississippi River south of Hannibal.Louisiana is at the junction of State Route 79 and US 54. The former follows the Mississippi River for most of its length from Hannibal to St. Charles County. The latter enters Louisiana from Illinois via the Champ Clark Bridge, named for a former US Speaker of the House from nearby Bowling Green.