Fort Terry, Plum Island

Fort Terry is a historic former U.S. Army coastal defense installation on Plum Island, just northeast of Orient Point in the Town of Southold, within Suffolk County. Established near the end of the 19th century, the fort was positioned to protect the eastern entrance to Long Island Sound and remained connected to American coastal defense through both World Wars.

Today, surviving brick barracks, gun batteries, military roads, utility buildings, observation structures, and other remnants of the installation remain scattered across Plum Island. Together they form the Fort Terry Historic District, which was added to the National Register of Historic Places in 2021.

History of Fort Terry

Fort Terry developed during a period when the United States was substantially strengthening its coastal defenses. Plum Island’s location near the eastern gateway to Long Island Sound made it strategically valuable because ships entering the Sound from the Atlantic passed close to the island.

The federal government acquired Plum Island around the turn of the 20th century for military purposes, and the Army developed Fort Terry as a Coast Artillery post. The fort was named for Major General Alfred H. Terry, a Union Army officer who served during the Civil War and later commanded U.S. forces in the West.

Fort Terry eventually became part of a larger network of coastal defenses guarding Long Island Sound. Other installations in the system included Fort H.G. Wright on Fishers Island and later military defenses farther east on Long Island. The New York State Military Museum describes Fort Terry as a coastal artillery fort that defended the approaches to Long Island Sound and remained associated with military operations from the late 1800s through the years surrounding World War II.

Gun Batteries and Coastal Defenses

Fort Terry was not a single fortress or enclosed castle. Instead, it consisted of numerous gun batteries, support buildings, barracks, roads, observation positions, and other military facilities spread across a large portion of Plum Island.

The installation included artillery intended to engage enemy vessels approaching Long Island Sound. Historic records identify weapons ranging from smaller rapid-fire guns to large disappearing guns and heavy mortars. Among the best-known installations were Battery Stoneman, Battery Steele, Battery Bradford, and several smaller batteries positioned around the island.

A federal review of Plum Island’s historic resources identified more than a dozen artillery batteries along with dozens of fire-control and observation structures, submarine mine-related facilities, searchlight shelters, power plants, barracks, a hospital, commissary, bakery, guard house, post exchange, chapel, and other supporting features associated with Fort Terry.

Fort Terry During World War I

Fort Terry was active during World War I, when coastal defense installations around Long Island Sound were placed on heightened military footing. Soldiers trained and served on Plum Island, while troops stationed at Fort Terry and nearby coastal posts were eventually sent overseas.

Historic photographs preserved by the Henry L. Ferguson Museum on Fishers Island show soldiers at Fort Terry, including troops gathered at the island’s dock before departing for France in 1918. Other surviving photographs document soldiers operating artillery and training around the fort before and during the war.

World War II

Fort Terry again served military purposes during World War II. The fort was used for training and coastal defense as concern increased over enemy submarines and possible attacks along the Atlantic Coast.

By this period, however, improvements in aircraft, naval weapons, radar, and other military technologies were rapidly reducing the importance of traditional fixed coastal artillery. After World War II, many American coastal forts were deactivated, including installations that had protected Long Island Sound for decades.

What Happened to Fort Terry?

The Army declared Fort Terry surplus in 1948, although the military later returned to the island for specialized research. In the early 1950s, portions of the former fort became associated with Army Chemical Corps research before responsibility for the island shifted to the U.S. Department of Agriculture.

In 1954, the federal government established the Plum Island Animal Disease Center, which became one of the nation’s principal facilities for studying foreign animal diseases and protecting the agricultural industry from infectious disease threats.

The research center occupied areas of Plum Island alongside many surviving Fort Terry structures. Some former military buildings were reused, while others remained largely untouched or deteriorated over time.

Fort Terry Historic District

The historical importance of the surviving military complex received formal federal recognition when the Fort Terry Historic District was listed on the National Register of Historic Places on March 29, 2021. The district is recognized for its significance in military history and engineering. National Park Service records identify the property as being on Plum Island in the vicinity of Southold, Suffolk County.

Federal documentation describes more than 100 historic improvements associated with Fort Terry across hundreds of acres of Plum Island. These include artillery batteries, fire-control structures, searchlight shelters, submarine mine facilities, power plants, military buildings, roads, parade grounds, and the island’s harbor infrastructure.

What Remains Today

Numerous remnants of Fort Terry remain visible on Plum Island. Large red-brick barracks buildings, concrete gun emplacements, former administrative and support structures, roads, and military infrastructure still provide evidence of the island’s decades as a coastal defense post.

Some buildings are heavily weathered or overgrown, while substantial concrete batteries remain embedded in the landscape. The surviving structures collectively make Fort Terry one of the more unusual preserved military landscapes in Suffolk County, particularly because the site has experienced relatively little conventional residential or commercial redevelopment.

Can You Visit Fort Terry?

Fort Terry is not currently open as a conventional public historic attraction. Plum Island remains a federally controlled site, and public access has historically been restricted because of the operations of the Plum Island Animal Disease Center and other federal facilities.

The federal government’s animal-disease research mission on Plum Island has been transitioning to the National Bio and Agro-Defense Facility in Manhattan, Kansas. As of 2026, USDA information continued to identify Foreign Animal Disease Diagnostic Laboratory operations on Plum Island while describing the ongoing transition to the Kansas facility.

Because access requirements and federal plans for Plum Island may change, visitors should not attempt to enter the island or Fort Terry without authorization.

Fort Terry and Plum Island

Fort Terry represents only one chapter in the much longer history of Plum Island. The island has also been associated with maritime navigation, the Plum Island Lighthouse, federal scientific research, wildlife habitat, and the distinctive waters surrounding Plum Gut and the eastern entrance to Long Island Sound.

Its isolation helped make Plum Island attractive for both military defense and later scientific research. At the same time, that restricted access contributed to the survival of archaeological sites, natural habitats, military structures, and historic landscapes that might otherwise have disappeared through development.

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Fort Terry, Plum Island

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Key Facts & Details

Name	Fort Terry
Location	Plum Island, Town of Southold, Suffolk County. New York
Type	Former U.S. Army coastal defense installation
Established	Late 19th century
Primary Role	Defense of the eastern entrance to Long Island Sound
Military Era	Spanish-American War era through World War II
Named For	Major General Alfred H. Terry
Historic Designation	Fort Terry Historic District
National Register	Listed March 29, 2021
National Register Reference	100006315
Notable Features	Gun batteries, barracks, observation structures, military roads, support buildings and former harbor facilities
Public Access	Restricted; not operated as a public historic attraction
County	Suffolk County

More than a century after its creation, Fort Terry remains an unusually intact reminder of the military importance once placed on the waterways surrounding eastern Long Island. Its abandoned barracks, concrete batteries and other surviving structures preserve a largely hidden chapter of Suffolk County history on one of Long Island’s most restricted and historically significant islands.