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 Karnack and Thebes.Former First Lady of the United States Lady Bird Johnson was born and reared in Karnack.The Caddo Lake National Wildlife Refuge, formerly the Longhorn Army Ammunition Plant, is located in Karnack.