Karnack is a rural unincorporated community in northeastern Harrison County near Caddo Lake in the eastern region of the U.S. state of Texas. The town is named after Karnak, Egypt. It was thought that the community's alignment with the city of Port Caddo was relative to that of Karnak and Thebes. The Caddo Lake National Wildlife Refuge founded in 2000, formerly the Longhorn Army Ammunition Plant in operation there from 1942 to 1997, is located in Karnack.