Originally a Native American sacred site: Troyville Earthworks Jonesville is the largest town in Catahoula Parish, Louisiana, United States, at the confluence of the Ouachita, Tensas, and Little rivers. The three rivers become the Black River at Jonesville, though the "Black" is primarily the continuation of the Ouachita River. A new bridge has been built over the Black River. After some miles, the Black flows into the Red River. The Jonesville population was 2,265 at the 2010 census. The parish seat is Harrisonburg to the north, which is actually smaller than Jonesville.