Plum Island is a barrier island located off the northeastern coast of Massachusetts, in the United States. It is a narrow, 11-mile-long strip of land that stretches from Newburyport in the north to Ipswich in the south, and separates the Atlantic Ocean from the mouth of the Merrimack River.

The island is known for its picturesque beaches, dunes, and marshes, which provide a habitat for a variety of plant and animal species, including piping plovers, least terns, and other shorebirds. Plum Island is also a popular destination for birdwatching, fishing, and other outdoor activities.

Despite its relatively small size, Plum Island has played a significant role in American history. During the Revolutionary War, the island was a key defensive position for the Continental Army, and it was the site of a battle between American and British forces in 1775. In the 19th and early 20th centuries, the island was used for farming and fishing, and it was a popular destination for summer vacationers. Today, it is a unique and cherished natural and cultural resource for the people of Massachusetts and visitors from around the world.