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 2020 census, DeRidder had a population of 9,852. It is the smaller principal city of the DeRidder-Fort Polk South CSA, a Combined Statistical Area that includes the Fort Polk South and DeRidder micropolitan areas, which had a combined population of 87,988 at the 2010 census.