In 1908, James M. Thomas, a native of Shamrock, Illinois, moved to this area and opened a store. He named the post office that he established on July 9, 1910 in honor of his home town. Between 1915 and 1916, the Sapulpa and Oil Field Railroad (later the St. Louis and San Francisco Railway) built a line northward from Depew to Shamrock. In 1916, the Atchison, Topeka and Santa Fe Railway constructed a line that connected Shamrock and Drumright. The railroad bypassed the town by three-fourths of a mile, so the citizens moved their businesses closer to the railroad. This developed Shamrock as a major shipping point for oil field equipment and crude oil. The town adopted an Irish theme, with streets named Tipperary, Dublin, Killarney, Blarney, and Cork.