Ballast Key, is the southernmost point of land in the continental United States. It is also the only privately owned land within the boundaries of the Key West National Wildlife Refuge, and was offered on the real estate market for US $13,800,000, as of February 2008 [1].

Located in the Outlying Islands of the Florida Keys, it is one of the Mule Keys that are 9 miles (15 km) west of Key West. The island's 13 acres are privately owned by David W. Wolkowsky through the David W Wolkowsky Trust.

The island had a cameo appearance in the Bond movie Licence to Kill.

The island features four bedrooms and a master suite with a fully equipped three bedroom guesthouse overlooking a palm tree lined beach. Water is supplied by desalination.

The island has two private residences.