St. Vincent Island is the westernmost of four barrier islands in the northwestern Florida Gulf coast which include Cape St. George Island, St. George Island and Dog Island. The island is located just offshore in Franklin County, Florida south southeast of Cape San Blas and north of Cape St. George Island close to the mouth of the Apalachicola River …St. Vincent Island is the westernmost of four barrier islands in the northwestern Florida Gulf coast which include Cape St. George Island, St. George Island and Dog Island. The island is located just offshore in Franklin County, Florida south southeast of Cape San Blas and north of Cape St. George Island close to the mouth of the Apalachicola River and the town of Apalachicola on the Florida Panhandle.