Fort Yamhill was a U.S. Army post built in 1856 in Oregon Territory near present-day Willamina to maintain a military presence beside the Grand Ronde Agency Coastal Reservation. Active until 1866, it was a large wooden outpost with a blockhouse, barracks, shops, hospital, and other support buildings; the hilltop blockhouse also served as a refuge for settlers. The post is notable for the service of several officers who later became Civil War generals, including Philip Sheridan, who helped supervise its construction. After abandonment, its blockhouse was moved and reused, while the site itself later gained preservation status and archaeological investigation.