High Quality Content by WIKIPEDIA articles! The Yamhill River is an 11-mile (18 km) tributary of the Willamette River, in the U.S. state of Oregon. Formed by the confluence of the South Yamhill River and the North Yamhill River about 3 miles (5 km) east of McMinnville, it drains part of the Northern Oregon Coast Range. The river meanders east past Dayton to join the Willamette River at its river mile (RM) 55 or river kilometer (RK) 89, south of Newberg.