Karnack is at the intersection of Farm roads 134 and 449, on the Louisiana and Arkansas Railway near Caddo Lake in northeastern Harrison County. Its name reportedly derived from the supposition that its distance from Port Caddo (the northeastern port of entry for the Republic of Texas) was the same as that of Karnak from Thebes in ancient Egypt. In 1898 a post office opened at Karnack, and the community shipped cotton and other commodities. Caddo Lake oilfields began producing in 1906. By 1915 the community had a population of 100, a general store operated by Thomas Jefferson Taylor, and a gristmill and cotton gin owned by W. H. Wurtzburger. In 1927 Karnack's population was estimated at 400. By the early 1940s the community reported a population of 850 and twenty-two businesses. In 1989 Karnack had twelve businesses, and in 1990 it reported 775 residents. The population remained unchanged in 2000. Lady Bird Johnson's childhood home, a two-story, white-brick house from the era of antebellum Texas, is at a site 2½ miles southwest of town on State Highway 43. Karnack became known from 1989 to 1991 because of the destruction of Pershing IA and II missiles at Longhorn Army Ammunition Plant there.