Ouachita is one of the 64 parishes in the state of Louisiana. It was formed in 1807, making it one of the original 19 parishes. As of the 2010 census, the population was 153,720. The county seat is Monroe, the 8th largest city in Louisiana. The parish has 633 square miles of area. The parish boundaries have been changed twenty-three times since the creation of the parish, the most changes of any parish in Louisiana.