Great Diamond Island

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Great Diamond Island is located 4 miles off the coast of Portland and has the smallest year round population of the islands serviced by Casco Bay Lines.  This quiet island’s population swells from a low of 50 in winter to 600 in summer.  With less than a square mile of area the island is crisscrossed with miles of dirt roads and foot paths, and is graced by 23 acres of protected Old Growth Forest.  The island is a granite outcropping with numerous small wet sand coves and a few small white sand beaches.  From October through May there are no public facilities, restaurants, or stores open.  The year round community relies on the City of Portland for groceries and other services.  Great Diamond Island is the only year round community in the bay that does not have a school or post office.  However, there is a volunteer fire department that is trained and supported by Portland.


This small island contains two distinct communities: the historic Cottage Community established in 1882 [Diamond Island Association] and Diamond Cove, the restored Ft. McKinley [Diamond Cove Homeowners Association]. In addition, there are approximately 100 acres of privately owned land [the former Deering Estate].

Although Great Diamond Island may have been a permanent settlement 2000 to 3500 years ago, according to archeological studies, in “recent” history it was a private island owned by Deacon Milk of Portland, who farmed and enjoyed the natural beauty of “Great Hogg Island,” followed by his heirs the Preble, Fessenden and Deering families. While the owners allowed the northerly end to be used for recreation, the island remained exclusively private until the US military purchased land on either side of Diamond Cove in the 1870s.

In a way, the Deering Farm shaped the island we know today. Diamond Island remained longest in the possession of a single family and was devoted entirely to farming – producing immense crops of hay.  Because the Diamonds were privately owned for so many years, they did not follow the traditional pattern of development of summer colonies. There were no large summer hotels and satellite cottages such as populated Peaks, Long, Cliff, Cushing, and Great and Little Chebeague. Although several cottages had been built on property leased from the Deerings, investors were reluctant to build a hotel on leased land.   Thus it was not until the Deering Heirs decided to sell a large part of Great Diamond, that summer colonies were developed on Great and Little Diamond.  The summer colony on Great Diamond was, therefore, by nature and circumstance, unlike other summer colonies on Casco Bay.

In 1882 an enterprising group of men from Portland, Maine, purchased a large tract of land (approx. 245 acres) on Great Diamond, reaching from Diamond Cove to the southwesterly segment of the island. Their intention was to establish a self-sufficient, planned community.  So they sold lots, established the Diamond Island Association, and changed the island’s name from Great Hogg (an indication of its former agricultural use) to Great Diamond Island, based partly on the ample supply of quartz crystals found on the island, but also surely to entice others to become property owners in the Diamond Island Association.  They had great plans for the island which included building their own wharf, the Casco Wharf; purchasing their own forty-five foot steam boat, the Isis; leasing the existing farm to furnish their own produce; establishing roads and areas for parks; setting up an acetylene gas production plant; erecting kerosene street lamps; establishing a water supply system; building a restaurant and meeting hall for association members; establishing a community store; and devising a set of by-laws which dictated how things would be.  A grand plan indeed, but one which they accomplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the late 19th and early 20th centuries remain and retain their shingled integrity and architectural beauty.  The streetlamps are electric, water and food come from the mainland, and the transportation system is public, but DIA’s Elwell Hall remains a gathering place for community suppers and other activities.  After two world wars and the loss of a portion of the original property for a military base, and the subsequent sale of Fort McKinley to a developer who appreciated a unique opportunity, the Diamond Island Association remains a vibrant community with both seasonal and year-round residents, and now shares the beautiful island with Diamond Cove Homeowners Association, our neighbors on the northerly portion of the island.

Despite 130+ years of changes and adaptations, DIA continues to be an attractive cottage community proud of its rural character, established traditions, and natural beauty.

Island Carts

Island Carts


Diamond Cove, formerly historic Fort McKinley, covers approximately 193 acres on the northern end of Great Diamond Island. Fort McKinley was constructed by the US government between 1891 and 1907 and was designed to defend Portland Harbor during the Spanish American War. Originally Fort McKinley consisted of over 125 buildings surrounding a military parade ground and was home to over 1000 soldiers and their families. In 1945 the US Army declared Fort McKinley surplus and it sat vacant until 1961 when it was sold to a private developer. It was not until 1984, after much disrepair and public controversy that restoration began by DicTar Associates and finalized by McKinley Partners into the private resort community of Diamond Cove we see today. Restored Fort McKinley, an historic era of US and island history, is on the National Historic Registry and as such it remains open to the general public. Pedestrian access only is allowed and restricted to Diamond Avenue and the Parade Ground. Viewing of the Gun Batteries and a narrated historic tour of Fort McKinley can be arranged by contacting DCHA (Diamond Cove Homeowner’s Association) management through their website at  Due to restrictions by DEP no motorized vehicles, except those exempted by and on file with the City of Portland, are allowed in or out of private Diamond Cove property.

Diamond Cove amenities include tennis courts, a two-lane bowling alley, an indoor basketball court, a heated pool, and many wet sand beaches, including Glass Beach, noted by Conde Naste Traveler to be one of the best sea glass hunting beaches in the world.  During the years that the property was under the military any glass items that became broken were ground up and pumped into the bay.  More than half a century later those broken bits adorn the sands of Glass Beach.  Diamond Cove also has a museum, restaurant and general store that are open to the public during the summer season, as well as a small inn.

The Parade Ground in Spring

The Parade Ground in Spring

If you plan to visit Great Diamond Island or Diamond Cove, bring your bike and a good pair of walking shoes, and remember to practice ‘leave no trace’ habits during your visit.