Guymon was planned in 1900 on a Rock Island Railroad survey by the Inter-State Land & Town Co. The Rock Island Railroad was built through the Oklahoma Panhandle in 1901. The town was founded as Sanford Post Office on 14 June 1901 and changed to Guymon Post Office on 29 June 1901 after E.T. Guymon, president of the Inter-State Land & Town Co. and owner of Star Mercantile, the town's first store. The townsite plat and deed were filed in 1904. Guymon was incorporated in 1905, and that was validated by a special act of the First State Legislature in 1908. Early Guymon was in Beaver County. In 1907 old Beaver County was split into Beaver, Texas, and Cimarron Counties, and Guymon was designated the Texas County seat. The present county courthouse was built in 1928.