Opelousas is a city in and the parish seat of St. Landry Parish, Louisiana, United States. It lies at the junction of Interstate 49 and U.S. Route 190. Opelousas is the principal city for the Opelousas-Eunice Micropolitan Statistical Area, Opelousas is also the 3rd largest city in the Lafayette-Acadiana Combined Statistical Area. At only 7.5 square miles, Opelousas is the most densely populated incorporated city in Louisiana. Founded in 1720, Opelousas is Louisiana's 3rd oldest city. The city served as a major trading post between New Orleans and Natchitoches in the 18th and 19th centuries.