Key Largo is an unincorporated area and census-designated place in Monroe County, Florida, United States, located on the island of Key Largo in the upper Florida Keys. The population was 12,447 at the 2020 census, up from 10,433 in 2010. The name comes from the Spanish Cayo Largo, or "long key". It is both the first island and town of the Florida Keys to be reached from the Overseas Highway to Key West. It was also the location of one of the stations of the Overseas Railroad.