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.

Monroe County is a county in the state of Florida. As of the 2020 census, the population was 82,874. Its county seat is Key West. Monroe County includes the islands of the Florida Keys and comprises the Key West-Key Largo Micropolitan Statistical Area. Over 99.9% of the county's population lives on the Florida Keys. The mainland, which is part of the Everglades, comprises 87% of the county's land area and is virtually uninhabited with only 17 people recorded in the 2020 census.