Pecos, the county seat of Reeves County, is on the western bank of the Pecos River, U.S. highways 80 and 285, Interstate Highway 20, and the Missouri Pacific Railroad, in the east central part of the county. It was established in the nineteenth century on the east side of the river as a camp for cattle drives up the river. In the 1880s the town was moved to the west side of the river and a plat was filed. However, a clear title to the land could not be secured. George A. Knight, who owned title to the section of land upon which the town was platted, offered the Texas and Pacific Railway a location for a depot and a gift of several town blocks. The railroad accepted his offer and built its tracks through the area in 1881. The town was called first Pecos Station, then Pecos City, and finally Pecos. In 1883 Reeves County was separated from Pecos County, and Pecos opened a three-room public school with fifty-two students. Pecos was named the county seat when Reeves County was organized in 1884. A post office was established the same year. In 1885 Pecos had a population of 150. In the 1890s the town developed a reputation for violence after several gunfights occurred there. During the 1899–1900 school term Pecos had one school, 111 students, and three teachers. A second school was added for the 1900–01 school term, when 148 students were taught by four teachers.
By 1904 the First National Bank of Pecos was opened to serve a population of 639. On June 11, 1907, the Pecos Mercantile Company was formed as a partnership by J. E. Bowen, Finley Holmes, and several out-of-town men. The population grew to 1,856 by 1914, but in 1925 it was 1,445. In 1928 it was 2,800. In 1929 the town had 4,000 residents and voted to incorporate. In 1931 Pecos had a population of 3,304 and 145 businesses. In 1933 the number of businesses had dipped to 110. In 1939 Pecos had a population of 4,800 and 190 businesses. With the advent of World War II and the building of area military installations, including Pecos Army Air Field, the population began a steady rise. In 1943 it surged to 6,500, but businesses flagged at 134. By 1952 Pecos had 8,054 residents and 338 businesses. The 1950s closed with a population of 14,200 and 272 businesses. During the 1960s Pecos had 13,000 residents and between 272 and 450 businesses and in 1970 a population of 14,960 and 340 businesses. During the 1970s and 1980s the population held around 13,000, but the number of businesses continued to fall. In 1990 Pecos had a population of 12,069 and fifty-five businesses. The town was a farming, ranching, and oilfield supply center and was home to the West of the Pecos Museum and to the annual West of the Pecos Rodeo. In 2000 the population was 9,501.