St. Augustine Beach is a city in St. Johns County, Florida, United States. The population was 6,803 at the 2020 US census, up from 6,176 at t…St. Augustine Beach is a city in St. Johns County, Florida, United States. The population was 6,803 at the 2020 US census, up from 6,176 at the 2010 census. It is part of the Jacksonville, Florida Metropolitan Statistical Area.