Coos Bay is an S-shaped inlet where the Coos River enters the Pacific Ocean, approximately 10 miles (16 km) long and two miles (three km) wide, on the Pacific Ocean coast of southwestern Oregon in the United States. The city of Coos Bay, once named Marshfield, was renamed for the bay and is located on its inner side. The Port of Coos Bay is the largest and deepest port between San Francisco, California and the Columbia River.Coos Bay is located in northern Coos County.