Key Largo is a census-designated place in Monroe County, Florida, United States, located on the island of Key Largo in the upper Florida Keys. The population was 10,433 at the 2010 census. The name comes from theSpanish Cayo Largo, or "long key". It is the first island of the Florida Keys and the originating point of theOverseas Highway to Key West. According to the United States Census Bureau, the CDP has a total area of 39.6 km² (15.3 mi²). 31.5 km² (12.2 mi²) of it is land and 8.1 km² (3.1 mi²) of it 20.54% is water.