Monroe (historically French: Poste-du-Ouachita) is a city in and the parish seat of Ouachita Parish, Louisiana, United States. As of the 2010 census, the city had a total population of 48,815, making it the ninth largest city in Louisiana. It is the principal city of the Monroe Metropolitan Statistical Area, which includes the parishes of Ouachita and Union. The two-parish area had a total population of 170,053 in 2000 and an estimated population of 172,275 as of July 1, 2007. The larger Monroe-Bastrop Combined Statistical Area is composed of both the Monroe Metropolitan Statistical Area and the Bastrop Micropolitan Statistical Area. The CSA had a population of 201,074 in 2000. Monroe and the neighboring city of West Monroe (pop. 13,250), which sits just across the Ouachita River, are often referred to as the Twin Cities of northeast Louisiana.

The settlement formerly known as Fort Miro adopted the name Monroe in honor of the steam powered paddle-wheeler James Monroe. The arrival of the ship had a profound effect on the settlers. It was the singular event that transformed the outpost into a town, in the minds of local residents. The ship is depicted in a mural at the main branch of the Monroe Library on North 18th Street. Therefore, credit is given to James Monroe of Virginia, the fifth President of the United States and, with Robert R. Livingston, one of the negotiators of the 1803 Louisiana Purchase from France, for whom the ship was named.