Blaine County is a county located in the U.S. state of Oklahoma. As of the 2020 census, the population was 8,735. Its county seat is Watonga. Part of the Cheyenne-Arapaho land opening in 1892, the county had gained rail lines by the early 1900s and highways by the 1930s. The county was named for James G. Blaine, an American politician who was the Republican presidential candidate in 1884 and Secretary of State under President Benjamin Harrison.

The Land Run of 1892 was the opening of the Cheyenne-Arapaho Reservation to settlement in the U.S. state of Oklahoma. One of seven in Oklahoma, it occurred on April 19, 1892, and opened up land that would become Blaine, Custer, Dewey, Washita, and Roger Mills counties. The land run also opened up what would become part of Ellis County, but was designated County "E" and then Day County prior to statehood.