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. Geography Key Largo is located at (25.106637, -80.429917). It shares the island of Key Largo with Tavernier to the southwest and North Key Largo to the northeast. U.S. Route 1, the Overseas Highway, runs the length of the community, leading north to Miami and southwest to Key West. According to the United States Census Bureau, the CDP has a total area of , of which are land and , or 20.96%, are water. Key Largo is the location of the first undersea park in the United States, established in 1963, and called the John Pennekamp Coral Reef State Park (located at Mile Marker 102). The park is primarily offshore and stretches into the Atlantic Ocean and is long. Adjacent to this is the Florida Keys National Marine Sanctuary covering 178 square nautical miles. Both areas were designed to protect marine life, including the extensive coral reefs in the area. Climate According to the Köppen climate classification, Key Largo has a tropical monsoon climate (Am). Demographics 2020 census As of the 2020 United States census, there were 12,447 people, 4,326 households, and 2,692 families residing in the CDP. The population density was 377.7/km2 (978.1/mi2). There were 8,043 housing units at an average density of 255.6/km2 (661.9/mi2). There were 4,326 households, out of which 23.7% had children under the age of 18 living with them, 50.5% were married couples living together, 7.4% had a female householder with no husband present, and 37.3% were non-families. 27.6% of all households were made up of individuals, and 8.8% had someone living alone who was 65 years of age or older. The average household size was 2.26, and the average family size was 2.75. In the CDP, the population was spread out, with 19.7% under the age of 18, 5.6% from 18 to 24, 28.7% from 25 to 44, 30.3% from 45 to 64, and 15.8% who were 65