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.

Running north of Route 18 for about 1 mile (1.6 km), the stream receives Klees Creek from the left and passes under the highway for the third time at Fort Hill.

[4][7] Continuing generally east and running between West Valley Highway on the left and Route 18 on the right, the river meanders slightly north of east, receiving Mill Creek from the right and Rock Creek from the left before reaching Sheridan at about RM 38 (RK 61).

About 1 mile (1.6 km) later, it passes under Route 18 for the fifth time and meanders generally east until turning north, still roughly parallel to the highway, at RM 30 (RK 48).

Shortly thereafter, the South Yamhill River passes under Oregon Route 99W and continues northeast toward McMinnville Municipal Airport.