Key Largo is an island in the upper Florida Keys archipelago and is the largest section of the keys, at 33 miles long. It is one of the northernmost of the Florida Keys in Monroe County, and the northernmost of the keys connected by U.S. Highway 1. Three census-designated places are on the island of Key Largo: North Key Largo, Key Largo and Tavernier. As o…Key Largo is an island in the upper Florida Keys archipelago and is the largest section of the keys, at 33 miles long. It is one of the northernmost of the Florida Keys in Monroe County, and the northernmost of the keys connected by U.S. Highway 1. Three census-designated places are on the island of Key Largo: North Key Largo, Key Largo and Tavernier. As of 2010, these three CDPs have a combined population of 13,850. None of Key Largo is an incorporated municipality; it is governed, at the local level, by Monroe County.