Cos Cob is a neighborhood and census-designated place in the town of Greenwich, Connecticut, United States. It is located on the Connecticut shoreline in southern Fairfield County. It had a population of 6,873 at the 2020 census. Cos Cob is located on the western side of the mouth of the Mianus River. The American Impressionist Cos Cob Art Colony flourished in the late 19th and early 20th centuries.