Bay St. Louis is a city in and the county seat of Hancock County, Mississippi, in the United States. Located on the Gulf Coast on the west side of the Bay of St. Louis, it is part of the Gulfport–Biloxi Metropolitan Statistical Area. As of the 2010 census, the city had a total population of 9,260.The city is recovering after population was lost in 2005 due to evacuations related to Hurricane Katrina. Many people stayed away from the city because of extensive damage from the storm surge. The Census Bureau's 2016 population estimate was 12,667.