Shamrock, on Interstate Highway 40 (here formerly U.S. Highway 66) in south central Wheeler County, was in the 1980s the largest town in the county. The name Shamrock was first suggested, for good luck and courage, by Irish immigrant sheep rancher George Nickel, when he applied in 1890 to open a post office at his dugout home six miles north of the present townsite. The name was accepted by federal postal officials, but this post office was never opened, probably because the Nickel home burned that same year. Another post office was operated nearby for a short while by postmistress Mary R. Jones. Shamrock had its official beginning with the arrival of the Chicago, Rock Island and Gulf Railway in the summer of 1902. In August, town lots were sold at the present townsite, which was then called Wheeler. When Frank Exum, who had recently opened a general store at his dugout-and-frame home, applied for a post office and named it after himself, the Shamrock post office was closed, but the railroad named the stop Shamrock in 1903, and the Shamrock post office reopened. That same year a school opened. From 1903 to 1907 Shamrock, Story, and Benonine competed as market and trade centers. By 1906 businesses from the other communities had moved to Shamrock. The Wheeler County Texan, begun at Story by T. C. Richardson in 1903, became the Shamrock Texan in 1928. By 1908 two banks had been chartered at Shamrock, and the Shamrock Cotton Oil Mill (later known as the West Texas Cotton Oil Company) was open for business. Shamrock was incorporated in 1911 with E. L. Woodley as the first mayor. In 1923 a water main laid from the nearby J. M. Porter ranch eliminated the need to haul water to town in barrels. Later, wells were dug. By 1925 the population had grown to 2,500. Oil was discovered in the area in 1926, and the population had increased to 3,778 by 1930.
Local natural gas wells operated by the Shamrock Gas Company gave the town a sufficient fuel supply, and the Texas Utility Company took over the lighting system. In addition to cottonseed oil mills, industry was provided by a compress, a carbon black plant, and a gasoline extraction plant. Just as the discovery of oil in 1926 had hastened the growth of Shamrock, a decline in the oil industry contributed to a decline in population to 3,123 by 1940; by 1950, however, the population had increased again, to 3,326. The improvement of U.S. Highway 66 made the main avenue of Shamrock boom with garages, filling stations, restaurants, and tourist courts; many of these later closed or moved out to the bypass after Interstate Highway 40 was completed. In the 1980s Shamrock continued to prosper. At that time it had modern schools, a chemical plant, several oil and gas processing plants, a hospital, and a nursing home. The population was listed at 3,113 in 1960, 2,644 in 1970, and 2,834 in 1980. In 1984 Shamrock reported a total of ninety-five businesses. Cattle, agriculture, gas, and petroleum continued to be primary in the economy. Ever since Glen Truax, the town bandmaster, started the tradition in 1938, Shamrock has had a St. Patrick's Day celebration on the weekend nearest March 17. This two-day affair features Irish food, fun, and festivities, complete with a parade, a banquet, various other entertainments, and the crowning of Miss Irish Rose. Shamrock is also the site of the annual Eastern Panhandle Livestock Show. A fragment of the genuine Blarney Stone from Blarney Castle in County Cork, Ireland, is mounted on a pillar in Elmore Park. The Pioneer West Museum, housed in the former Reynolds Hotel, a typical drummer's hotel of the 1920s, features exhibits on city and county history. In 1990 the population of Shamrock was reported as 2,286. The population was 2,029 in 2000.