After the Civil War, several frontier forts in Texas (such as Belknap, Worth and Cooper) were abandoned, and new ones established further west. One of these new forts was Fort Griffin, which opened in 1867. Its original location may have been at Young and Stephens counties, but it was moved west along the Clear Fork of the Brazos River to occupy a site at the border of Throckmorton and Shackleford counties. Along with Fort Richardson, which lay just to the northeast of Fort Griffin, these forts marked the boundary line ("the frontier") between Native American lands and white settlement ("civilization") from Indian Territory all the way to the Rio Grande at Fort Davis.
The words "frontier" and "civilization" when used within the context of western history are problematic. These terms denote that Native people weren't Americans, and that whites were a superior culture. It's an archaic world view that historians now refrain from using except when discussing the language of the era.
Erected on top of a hill in the beautiful, scrubby countryside just west of the Cross Timbers, Fort Griffin allowed white Texans to settle Comanche country. A rough and tumble town nicknamed the "Flat" appeared at the north side of Fort Griffin's hill, where saloons and bawdy houses competed for the soldier's business. In the late 1870s, the Great Western Trail had a stop at the Flat before pushing further north towards Dodge City, Kansas. The town's businessmen "cleaned up" its reputation in the 1880s, and campaigned to make the town of Fort Griffin the county seat. However, Albany, with its proximity to the railroads and heavy local investment, became the seat instead.
The antebellum Camp Cooper, where both the Robert E. Lee and William Tecumseh Sherman served, lay just northwest of Fort Griffin in southern Throckmorton County. Established in 1854, the camp's purpose was to protect a reservation for a band of peaceful Comanches against the hostile whites. A Comanche School was founded nearby. But the white settlers terrorized them until the band was forced into Indian Territory. In 1860, the Comanche Chief Peta Nocona was killed along the Pease River in the Caprock, and his wife, Cynthia Ann Parker, was re-captured and brought back to the camp. (Cynthia Ann was a pioneer's daughter who had been kidnapped during a raid on Parker's Fort in the 1836). Cynthia Ann's son Quanah led the remaining Comanches during the Red River Wars.
After the Red River Wars of 1871-1874, federal law prohibited Native Americans who once called Texas home from crossing south of the Red River. The United States closed Fort Griffin, though The Flat hung on for a while until it, too, succumbed to population loss.
Today, the site is a state historical park that is also home to the official state longhorn herd. The town of Fort Griffin (the "Flat") sits on private but accessible land. The site of Camp Cooper lies on private land and from what I gather, nothing visible remains except a historic marker from 1936.