Fort Yamhill was one of several forts in western Oregon established after hostilities between Native Americans and settlers led to treaties and the creation of the Grand Ronde Reservation. Forts such as Yamhill and Hoskins were built to keep the peace, protect Native people and settlers, and enforce reservation boundaries and rules. The first troops moved in after Indian Agent Joel Palmer requested military assistance because he feared angry white settlers would overrun reservation land. Their stated purpose was to maintain a temporary camp, protect Indians and settlers from one another, and enforce rules. After two years, the post had more than twenty buildings, and its soldiers enforced the Line of Demarcation that kept settlers and Indians separate, allowing no one to cross without permission. By 1858, Col. J.K.F. Mansfield reported quarters for one company of soldiers, more than enough officers' quarters, a blockhouse, a quartermaster and commissary storehouse, a guardhouse and prison, a hospital, laundresses' houses, a bake house, stables, a barn, smith's and carpenter's shops, and a sutler's store.