Key Largo is an island in the upper Florida Keys archipelago and, at 33 miles (53 km) long, the largest of Keys. It is also the northernmost of the Florida Keys in Monroe County .

Key Largo is connected to the mainland in Miami-Dade County by two routes. The Overseas Highway, which is U.S. Route 1, crosses Jewfish Creek from the middle of the island to the extreme southeastern part of the mainland, while the Card Sound Bridge connects the northern part of the island across Biscayne Bay to the mainland. Both routes lead to Florida City .

Key Largo is situated between Everglades National Park to the north-west and John Pennekamp Coral Reef State Park to the east, the first underwater park in the and the site of the only living coral barrier reef in the continental .

Key Largo is a census-designated place and town in Monroe County, Florida, located on the island of Key Largo , in the upper Florida Keys . As of the 2000 census, the town had a total population of 11,886. The name comes from the Spanish Cayo Largo , or "long key". It is the first island of the Florida Keys and the originating point of the Overseas Highway to Key West .