Marco Island is a city in Collier County, Florida, United States, located on an island by the same name in the Gulf of Mexico off the coast of Southwest Florida. It is a principal city of the Naples–Marco Island Metropolitan Statistical Area. The population was 12,879 at the 2000 census.Originally named San Marco Island by Spanish explorers, Marco Island is the largest barrier island within Southwest Florida's Ten Thousand Islands area extending southerly to Cape Sable. The climate is subtropical with distinct wet and dry seasons, with most of the rainfall falling between the months of June and October.