Key Largo is an island in the upper Florida Keys archipelago and, at 33 miles (53 km) long, the largest of the Keys. It is also the northernmost of the Florida Keys in Monroe County, and the northernmost of the Keys connected by U.S. Highway 1. Its earlier Spanish name was Cayo Largo, meaning Long Key. Key Largo is connected to the mainland in Miami-Dade County by two routes. The Overseas Highway, which is U.S.