Dairy Creek is a 10.55-mile (16.98 km) tributary of the Tualatin River in the U.S. state of Oregon. It begins at the confluence of its east and west forks near the unincorporated community of Schefflin and meanders southeast across the Tualatin Valley to the Tualatin River near Hillsboro, in Washington County. East Fork Dairy Creek begins at 45.788446°N 123.041498°W (Dairy Creek East Fork source) in Columbia County, slightly north of its border with Washington County, and flows generally south for 22 miles (35 km). West Fork Dairy Creek, also about 22 miles (35 km) long, forms at 45.7553899°N 123.178168°W (Dairy Creek West Fork source), near the unincorporated community of Tophill, and flows generally southeast.