Dimmitt, the county seat of Castro County, is on U.S. Highway 385 fifty-five miles southwest of Amarillo in the central part of the county. In March 1890 the Bedford Town and Land Company, headquartered at Sherman, in Grayson County, bought a section of land near the center of the county and laid out a townsite. H. G. Bedford handled the sale of lots at the new site, which the promoters named for their colleague and Bedford's brother-in-law, Rev. W. C. Dimmitt. During 1890 other promoters, including Ira Aten and Lysius Gough sought to develop rival townsites as candidates to be county seat. But on December 18, 1891, Dimmitt was elected.
By that time Dimmitt had two stores, a post office, and a resident doctor. J. W. Carter, the county's first resident, established a hotel, and Miss Lou Belsher taught the first school. A Baptist church was established, and several different communions met in the schoolhouse. William Andrew (Uncle Buck) Tate established a lumber and wagon yard and later opened a second hotel. Aten waged unceasing war against cattle rustlers during his tenure as county sheriff. In 1892 a wooden frame courthouse was completed; it was used until 1906, when fire caused by lightning destroyed it. An elaborate brick structure replaced it in 1908. By then "Old Man" Callahan had started the Plainsman, the county's first newspaper, and C. E. McLean had opened the First State Bank of Dimmitt. A brick school building was completed in 1910. Although the town was for several years without a railroad and growth was relatively slow, it remained the county seat. In July 1928 the Fort Worth and Denver South Plains Railway was extended to Dimmitt. As a result the town of between 800 and 1,000 residents was incorporated, and the Castro County News succeeded the defunct Plainsman. During the 1930s a hospital and a county library were established. The present county courthouse replaced the earlier red-brick building in 1938. By 1940 Dimmitt was booming as the county's main trading point with a population of 943. The population increased to 1,441 by 1950. Dimmitt High School developed a well-earned reputation for its basketball teams, amassing a total of seven state championships between 1952 and 1992.
Dimmitt, which had 233 businesses in 2000, depends upon the county's variety of agricultural products for most of its income. Cargill Inc. produces syrups and other corn products. Plants in Dimmitt process lettuce, onions, potatoes, and carrots. Cattle and sheep are fed in the county's numerous feedlots. The Dimmitt Goodpasture Plant, a one-time superfund site, produces anhydrous ammonia and agricultural chemicals. Other industries include grain elevators and cotton gins and the manufacture of farming equipment. A federal youth corps project was located in Dimmitt in the 1970s. The city's resources include the Plains Memorial Hospital and Nursing Home, the Rhodes Memorial Library, the Castro County Country Club, a city park, and a radio station. Dimmitt Municipal Airport, just north of town, has facilities for both charter and agricultural services. The Castro County Historical Museum houses relics from the past in the Jeff Gilbreath farmstead, dating from 1909. It features craft exhibits and demonstrations during the county fair in September. Other annual events include a chamber of commerce banquet in January, a square dance and stock show in February, and a rodeo in June. Former state senator and United States congressman Kent Hance came from Dimmitt, which grew in population from 4,327 in 1971 to 5,019 in 1980. Since that time the population has declined somewhat, falling to 4,408 in 1990 and 4,375 in 2000. In 2016 the population was estimated at 4,199.