Duck Key is a census-designated place in Monroe County, Florida, USA; it has a land area of 0.9 square miles. It is a small island located at mile marker 61 in the upper end of the Lower Keys just off the U.S. Overseas Highway 1.

The place was the site of salt manufacturing operation in the 1820s and 1830s. After the hurricane of 1935, it ceased its operations and just resumed when the key was connected to the highway by a causeway in 1953. The island is formerly a salt industry but later it was transferred to Key West, managed and owned by Mr. Howe, who is also owner of this key. Hawk's Cay Resort is built in this island, and this is sometimes known by that name.

There are also several unique attractions found in the Key, when visitors leave the US highway 1, they pass through a landscaped stone entrance way that looks like an old Spanish gateway that once led into the city of St. Augustine. Another is the scenic arched bridges with their balusters and urns, and the canals which flow under the bridges. The architecture in the island is also astounding; most of the buildings and residences are inclined by West Indian design.

Every year Duck Key holds a "Welcome Back Snowbird Party," this celebration is dedicated to many island residents who travel north during summer and return in the island during the fall.