The Coos Bay Mosquito Fleet comprised numerous small steamboats and motor vessels which operated in the late 19th and early 20th centuries on Coos Bay, a large and mostly shallow harbor on the southwest coast of the U.S. state of Oregon, to the north of the Coquille River valley. Coos Bay is the major harbor on the west coast of the United States between San Francisco and the mouth of the Columbia River.

Coos Bay is a city located in Coos County, Oregon, United States, where the Coos River enters Coos Bay on the Pacific Ocean. The city borders the city of North Bend, and together they are often referred to as one entity called either Coos Bay-North Bend or Oregon's Bay Area. Coos Bay's population as of the 2020 census was 15,985 residents, making it the most populous city on the Oregon Coast. Oregon's Bay Area is estimated to be home to 32,308.