Knox County is in the Rolling Plains region of northwest central Texas, bordered on the north by Foard County, on the east by Baylor County, on the south by Haskell County, and on the west by King County. Its center point is 99°45' west longitude and 33°35' north latitude, about seventy-five miles north of Abilene. The county was named for Henry Knox, the secretary of war in George Washington's first cabinet. Knox County embraces 854 square miles of level to rolling, mesquite-covered plains, dissected by hilly ranges and eroded breaks; altitudes range from 1,401 to 1,646 feet above sea level. The area is drained by the North Wichita River along most of its northern border, and by the South Wichita and Upper Brazos rivers, which cross the county. The soils, ranging from black waxy to sandy loam, are good for both farming and stock raising. Temperatures range from an average minimum of 28° F in January to an average maximum of 98° in July. The annual rainfall is 24.64 inches, and the average growing season lasts 217 days. Two railroad lines, owned by the Santa Fe and Burlington Northern companies, serve the county, and the area is crossed by two U.S. highways (82 and 277), three State highways (6, 114, and 222) and several farm-to-market roads.
Until the late nineteenth century, the area now known as Knox County was frequented by nomadic Indians who followed the herds of buffalo that roamed the region. In Spanish and Mexican Texas, several copper deposits along the Brazos were reportedly mined by Spaniards using Indian conscripts as laborers. The first Anglo to penetrate the future county area was probably Capt. Randolph B. Marcy, who in 1854 traveled through the area to survey the Brazos and Wichita valleys while searching for a suitable site for an Indian reservation. In 1855 elements of the Second United States Cavalry, commanded by colonels Albert Sidney Johnston and Robert E. Lee, patrolled the vicinity.
In February 1858 the Texas legislature formed Knox County from lands formerly assigned to Young and Bexar counties; because the area remained unsettled, it was again decreed a county in 1876 and attached to Baylor County in 1879 for administrative purposes. In 1880 only three farms or ranches were in operation in the county, and the census counted seventy-seven residents. Settlers came in larger numbers between 1880 and 1900. Robert D. Goree, who came as a cattleman to Northwest Texas in 1882, opened up the land to agriculture by encouraging people from older states and other Texas counties to move into Knox County. The county was organized in 1886, with the town of Benjamin, founded by Hillary Bedford in 1884 and named for his oldest son, as county seat. The first courthouse, a small box-and-strip building, was replaced by a native stone structure in 1888. By 1887 Goree had established a small settlement that he named after himself at Riley Springs, in the southeastern part of the county, and in 1895 a colony of German Catholics established the town of Rhineland a few miles away. Several ranchers, including Robert B. Masterson, Tom (William Thomas) Waggoner, W. R. McFadden, and J. C. Teague, had all or part of their ranges in the county. By 1890 there were seventy-six farms and ranches in the county, and by 1900 there were 366, encompassing about 449,000 acres. Though almost 39,400 cattle were reported in the county in 1900, farming was becoming more firmly established. The number of acres devoted to corn production, for example, rose from about 1,500 in 1890 to more than 7,300 by 1900; during that same period, wheat acres in the county grew from 603 to 13,188, and cotton acres from 336 to 2,135. Meanwhile, the population of the county had increased to 1,134 by 1890 and to 2,322 by 1900.
Further movement to Knox County was encouraged during the first years of the twentieth century, when two railroads built their tracks into the area. In 1905 the Wichita Valley Railroad entered the county; the Kansas City, Mexico and Orient line followed suit in 1907. By 1910 the county had 1,175 farms and ranches. The population had increased to 9,625. Corn was planted on almost 25,000 acres by that time, and cotton on more than 36,000 acres. Meanwhile, wheat production also increased, and Knox County farmers were diversifying into fruit and poultry production. By 1910 more than 33,000 fruit trees (mostly peach) had been planted in the county, and almost 41,000 fowl were reported on local farms.
Between 1910 and 1920 some of the earlier settlers were shaken out, as the number of farms dropped to 1,037 by 1920, when the population had declined to 9,240. The county grew again during the 1920s, however, largely because of a continuing cotton boom. Between 1910 and 1929 corn and wheat culture increasingly gave way to cotton culture, which became the center of the local agricultural economy. In 1919 53,645 acres was planted in cotton, and by 1930 production of the fiber had expanded to 130,247 acres. By 1930 there were 1,460 farms in Knox County, and 11,368 people were living there. But Knox County agriculture suffered serious setbacks during the Great Depression and the Dust Bowl. Cotton production plunged more than 50 percent, and by 1940 only 67,584 acres was planted in the fiber. About a third of the county's farmers left their lands during this period; by 1940 only 980 farms remained. The population also dropped during the 1930s, to 10,090 in 1940.
Oil was discovered in Knox County in 1945. By 1946 the county's first successful oil well had been spudded on the Beavers Ranch, north of Benjamin; in subsequent years other wells were drilled in the southern part of the county. In 1948 oil production was only thirty-seven barrels, but in 1956 it reached 978,715, and in 1960, almost 2,415,000. County oil wells produced 2,065,000 barrels in 1965, 771,089 barrels in 1974, and 1,421,964 barrels in 1982. Production totaled about 888,000 barrels in 1990, and by January 1, 1991, almost 55,881,000 barrels had been taken from Knox County lands since discovery in 1945.
After the 1940s the mechanization of agriculture combined with other factors to continue depopulating the county. After 1940 the population dropped to 10,082 in 1950, 7,857 in 1960, 5,972 in 1970, and 5,329 in 1980. In 2014, 3,858 people were living in the county. Of those, 60.1 percent were Anglo, 6 percent African American, and 32.8 percent Hispanic. In national presidential elections between 1952 and 1992 Knox County went Republican only twice, in 1972 (Richard Nixon) and 1984 (Ronald Reagan). In 1988 Knox County was one of fifty-nine Texas counties still legally dry. The county remains largely a farming and ranching area. In the mid-1980s cultivated acres in the county totaled about 33,000 acres, producing cotton, wheat, grain sorghums, guar (a forage crop), and truck crops, which accounted for a large part of the $23 million farm income averaged annually between 1980 and 1988. During the 1985–86 season, the county's four active gins processed 21,982 bales of cotton. Beef cattle and sheep are also important factors in the county's agricultural income. Benjamin (population, 247), the county seat, is a trade and market center; in Munday (1,191), the largest town, is the Texas A&M Vegetable Research Center. The county hospital and a United States Department of Agriculture plant-materials research center are located in Knox City (1,040). Other communities include Goree (192), Rhineland, Truscott, Vera, and Hefner. Several small reservoirs near Benjamin provide recreation.