OAK BRANCH. Oak Branch rises within Fort Hood Military Reservation in southeastern Coryell County near the Bell County line (at 31°10' N, 97°41' W) and runs northeast for 4½ miles, through western Bell County, to its mouth on Cowhouse Creek, six miles north of Killeen (at 31°12' N, 97°37' W). The creek, named for the post oak trees native to the area, flows through gently sloping to sloping and undulating to rolling terrain and lies entirely in Fort Hood.