Key West is a coral cay island situated in the Straits of Florida at the southernmost end of the United States state of Florida. It forms part of the outlying Florida Keys archipelago and, together with adjacent islands like Fleming Key and Stock Island, constitutes the City of Key West. The city serves as the county seat of Monroe County, which encompasses a majority of the Florida Keys and part of the Everglades. Its strategic location makes it the southernmost city in the contiguous United States and the westernmost island in the chain connected by highway.

The island was originally inhabited by Native American tribes, including the Calusa and Tequesta, before first recorded European contact in 1513 by Juan Ponce de León. After periods of Spanish and British control, it became U.S. property in 1822 following a claim by Lt. Commander Matthew C. Perry. The island rapidly developed into a major maritime center during the 19th century, driven by its strategic position along shipping lanes and a thriving wrecking industry that made it one of the wealthiest communities in the nation per capita.

The city is defined by its main commercial corridor, Duval Street, which runs from the Gulf of Mexico to the Atlantic Ocean. It functions as a major transportation hub hosting a passenger cruise port, an international airport, and Naval Air Station Key West. The island lies within the Florida Keys National Marine Sanctuary and is near protected areas like Dry Tortugas National Park. Its proximity to the Great Florida Reef establishes it as a notable center for recreational diving and tourism.

Key West maintains a unique cultural identity, notably through the symbolic Conch Republic independence declared in 1982, which is celebrated annually in April. The city carries the motto One Human Family and features historic sites such as St. Mary’s Star of the Sea Catholic Church, built in 1852, and the Basilica School of Saint Mary Star of the Sea. These landmarks reflect the island's religious and educational development alongside its maritime heritage.

The population was 26,444 as of the 2020 census. The economy relies heavily on tourism and transportation, with the city serving as the southern terminus of U.S. Route 1. Key West experiences a mild, tropical climate characterized by dry and wet seasons, with abundant sunshine from November through April. It claims to be the only city in the lower forty-eight states to have never recorded frost or snowfall.