Great Diamond Island ferry: two landings, one former Army fort

Ten boats a day leave Portland for the Great Diamond landing this fall, and eight for Diamond Cove. The gap between those two numbers is the first thing to understand about Great Diamond Island. It is one island in Casco Bay, legally part of the City of Portland, but it has two public floats, and Casco Bay Lines treats them as two stops with their own timetables. The 05:00 and 15:15 departures, for example, go to Great Diamond and skip the cove altogether.

Which landing you want depends on why you are going. The Great Diamond float, on the southwest shore opposite Little Diamond Island, serves the homes outside the old fort and an island with only a limited network of roads. Diamond Cove, on the northeast shore, is the restored Fort McKinley: a private community of converted barracks and officers' houses, plus the restaurants, the inn and the museum that most day visitors come for. The two are linked by island roads, not by a boat shuttle.

The same operator runs the busier Portland–Peaks Island crossing from the same pier, and the ticketing rules are identical, so this page leaves those out and concentrates on the Diamond side: when boats call at each landing, what the fall table does on Fridays, and what happens to a car.

The fall table at both landings, with Friday nights running later

Fall schedule, September 8 – October 12, 2026; read from Casco Bay Lines on September 25, 2026   Casco Bay Lines — Great Diamond Island and Diamond Cove schedules (fall) · 2026-09-25

Priced like any inner-bay island, and a car only by request

The district lists Great Diamond Island and Diamond Cove as two separate rows in its fare table and then charges exactly the same for both, and the same as every other inner-bay island. What you buy in Portland covers both directions, and nobody asks for anything at either island float on the way home. The ticket is good for 60 days, provided its season matches the date of the trip.

A car is a different transaction altogether and is not sold at the passenger window; see the notes under the table.

Peak season April 18 – October 12, 2026; off-peak October 13, 2026 – April 16, 2027   Casco Bay Lines — Ferry Passenger Fares · 2026-09-25

Commercial Street, the southwest float and the cove below the fort

Out past Little Diamond to the cove below Fort McKinley

From Commercial Street the boats head east into Casco Bay, past the Portland waterfront and out toward the cluster of Diamond islands, a trip the operator times at 15 minutes to Little Diamond and 20 to 25 to Great Diamond. Diamond Cove is on the far, northeastern shore, so the operator allows it a much wider window of 30 to 45 minutes, depending on the route a boat takes and how much cargo it is working.

The return tables hint at the order of calls. Where a boat stops at Diamond Cove on the way back, it leaves the Great Diamond landing 10 to 30 minutes later, and Little Diamond five minutes after that. So on a weekday afternoon the 17:05 from the cove, the 17:15 from Great Diamond and the 17:20 from Little Diamond are best read as a single boat sweeping back toward the city.

Golf carts, a gated community and a restaurant on summer hours

• Name the landing when you plan

  The restaurants, the Inn, the museum and the holiday rentals the operator lists are all at Diamond Cove. If you are staying with someone outside the old fort, ask which float they use before you pick a boat, because the two landings run to different timetables.

• Diamond Cove is private beyond the avenue

  Visitors may walk up Diamond Avenue to the restaurants, the museum and the lodging, but the parade ground, the parks, the beaches and the private roads are closed to anyone without an escort. Tours of the fort grounds are by reservation.

• Diamond's Edge closes with the summer

  The restaurant in the old Quartermaster's storehouse opens from late May to late September, so by the end of this month an evening boat to the cove may find its kitchen already shut for the year.

• No gasoline cars at the cove

  Diamond Cove allows maintenance vehicles and electric golf carts, nothing else with an engine, and the rest of the island gets around by cart and bicycle. A visitor on foot is the norm, not the exception.

• Watch Friday

  The late boat shifts on Fridays: Portland to the island at 21:15 instead of 20:30, and the last departure off Great Diamond at 23:15 instead of 22:35.

• Bikes pay, dogs pay

  A bicycle is $7.00 round trip for an adult and a leashed dog $4.50. Dogs riding in a pet carrier travel free, and so do service animals.

A coastal fortress that turned into a Portland neighborhood

Fort McKinley went up between 1891 and 1907 as part of the coastal defenses around Portland Harbor, prompted by the Spanish-American War, and at its peak it housed more than 1,000 soldiers in brick barracks around a parade ground. The Army retired it in 1945. Decades later the buildings were restored as private homes, with slate roofs and wooden porches intact, and Diamond Cove as a whole now carries a National Register listing. The concrete gun batteries still stand in the woods at the eastern end, off-limits on safety grounds.

The boats that serve the fort's old wharf descend from the steamers that began scheduled island service around 1870. The private Casco Bay Lines of the twentieth century collapsed into bankruptcy in 1981, and the Maine Legislature set up a public transit district that April to keep the islands connected; it ran its first boats on March 27, 1982. Among the New England routes covered here, no other island has two stops on separate tables; the Isle au Haut mailboat, with its two landings, shares the pattern only at a smaller scale. The district that runs these boats is, like the elected ferry district serving Fishers Island, a public body set up to keep islands connected.

Settling the Great Diamond or Diamond Cove question