The Whitehorse Ranch is a historic cattle ranch in Harney and Malheur counties in the southeastern corner of Oregon, United States. The ranch was started in 1869 by John S. Devine, a well-known 19th-century cattle baron. It was originally the headquarters for the Todhunter and Devine Cattle Company. The ranch has been in the cattle business continuously since it was founded. Today, the Whitehorse Ranch includes 63,222 acres (255.85 km2) of deeded property and grazing rights on an additional 287,205 acres (1,162.28 km2) of public range land administered by the Bureau of Land Management.