South Yamhill River

South Yamhill River
Bridge over the river at Sheridan
Name origin: Uncertain but probably after a local Kalapuya tribe
Country	United States
State	Oregon
Counties	Polk and Yamhill
Source	Northern Oregon Coast Range
- location	Siuslaw National Forest, in western Yamhill County, Oregon
- elevation	551 ft (168 m)
- coordinates	45°06′38″N 123°43′40″W / 45.11056°N 123.72778°W / 45.11056; -123.72778
Mouth	Yamhill River
- location	between McMinnville and Dayton, Yamhill County, Oregon
- elevation	75 ft (23 m)
- coordinates	45°13′33″N 123°08′41″W / 45.22583°N 123.14472°W / 45.22583; -123.14472Coordinates: 45°13′33″N 123°08′41″W / 45.22583°N 123.14472°W / 45.22583; -123.14472
Length	60 mi (97 km)
Basin	492 sq mi (1,274 km2)
Discharge	for McMinnville, Oregon, 5.6 miles (9.0 km) from mouth
- average	1,801 cu ft/s (51 m3/s)
- max	47,100 cu ft/s (1,334 m3/s)
- min	0.58 cu ft/s (0 m3/s)
Location of the mouth of South Yamhill River in Oregon

The South Yamhill River is a tributary of the Yamhill River, approximately 60 miles (97 km) long, in northwest Oregon in the United States. It drains an area of the Northern Oregon Coast Range, as well as part of the Willamette Valley west of the Willamette River.

The South Yamhill River rises at an elevation of 551 feet (168 m) above sea level and falls 476 feet (145 m) between source and mouth to an elevation of 75 feet (23 m). It begins at the confluence of Hanchet Creek and Kitten Creek in the Siuslaw National Forest of the Northern Oregon Coast Range. The source, at about river mile (RM) 60 or river kilometer (RK) 97 lies near the border between Tillamook and Yamhill counties west of the Grand Ronde Community, an Indian reservation. Flowing southeast on the north side of Oregon Route 22 in Yamhill County, the river receives Pierce Creek and Ead Creek from the , and Cedar Creek from the before flowing under the highway at about RM 57 (RK 92). Continuing parallel to the highway, which lies to its left, the river receives Crooked Creek from the left and Elmer Creek from the right before passing Midway and entering Polk County at about RM 55 (RK 89). Just beyond the county border, Agency Creek enters from the left. About 1 mile (1.6 km) later, the river receives the Rogue River from the left, reaches Grand Ronde, and passes under Grand Ronde Road and Oregon Route 18, a highway connecting the Portland metropolitan area to the Oregon Coast. Shortly thereafter, Rock Creek enters from the right.