DeRidder is a city in, and the parish seat of, Beauregard Parish, Louisiana, United States. A small portion of the city extends into Vernon Parish. As of the 2010 census DeRidder had a population of 10,578. It is the smaller principal city of the DeRidder-Fort Johnson South CSA, a Combined Statistical Area that includes the Fort Johnson South and DeRidder micropolitan areas, which had a combined population of 87,988 at the 2010 census.