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.

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.