Key Largo is an island in the upper Florida Keys archipelago and is the largest section of the keys, at 33 miles (53 km) 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 (CDPs) 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.

The Florida Keys are a coral cay archipelago off the southern coast of Florida, forming the southernmost part of the continental United States. They begin at the southeastern coast of the Florida peninsula, about 15 miles (24 km) south of Miami and extend in a gentle arc south-southwest and then westward to Key West, the westernmost of the inhabited islands, and on to the uninhabited Dry Tortugas. The islands lie along the Florida Straits, dividing the Atlantic Ocean to the east from the Gulf of Mexico to the northwest, and defining one edge of Florida Bay. The southern part of Key West is 93 miles (150 km) from Cuba. The Keys are located between about 24.3 and 25.5 degrees North latitude.