The area is named for the Pecos River, which flows along the northern boundary of the county. The land of Pecos County was originally in Bexar Territory and later part of Presidio County. Pecos County was established by the Texas legislature in 1871. The county was formally organized on March 9, 1875, at St. Gall, which became the county seat. During the 1880s St. Gall was renamed Fort Stockton, and the army post closed. In 1883 parts of the county land was split off to form Reeves and Terrell counties, and in 1885 another part was incorporated into the new Val Verde County. -Handbook of Texas Online: Pecos County