Monroe is a city in and the parish seat of Ouachita Parish, Louisiana, United States. As of the 2000 census, the city had a total population of 53,107, making it the eighth largest city in Louisiana. A July 1, 2007, United States Census Bureau estimate placed the population at 51,208. 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.