Brazos River, a river in Texas. It is formed by the junction of two main head-streams, the Double Mountain Fork and the Salt Fork, in Stonewall County. The Brazos flows generally southeast across the state, past Waco to the Gulf of Mexico near Free-port. Its length is about 1,310 miles (2,110 km). Possum Kingdom and Whitney dams are the largest of several flood-control, power, and irrigation projects on the river.