Casco Bay Lines is a publicly run transportation company that services the residents of the islands of Casco Bay. These islands include Peaks Island

Peaks Island, Maine

Peaks Island is the most populous island in Casco Bay, Maine. It is part of the city of Portland and is approximately from downtown. The island became a popular summer destination in the late 19th century, when it was known as the Coney Island of Maine, home to hotels, cottages, theaters, and...

, Little Diamond Island

Little Diamond Island, Maine

Little Diamond Island is an island in Casco Bay Maine. It is part of the city of Portland, Maine. As of the 2000 census, the island had a year-round population of 5. Most of the island is private property. It is served by the Casco Bay Lines ferry service.At low tide, Little Diamond Island...

, Great Diamond Island

Great Diamond Island, Maine

Great Diamond Island is an island in Casco Bay, Maine. It is part of the city of Portland, Maine. As of the 2000 census, the island had a year-round population of 77. The island is not accessible from the mainland by motor vehicle and has a limited network of roads. The primary modes of...

, Diamond Cove, Long Island

Long Island, Maine

Long Island is an island town in Cumberland County, Maine, United States, which seceded from the city of Portland in 1993. The population was 202 at the 2000 census...

, Chebeague Island

Chebeague Island, Maine

Chebeague Island is an island town in Cumberland County, Maine, United States, located in Casco Bay, 10 miles from Portland. These islands are sometimes referred to as an older, now archaic term "The Calendar Islands" because there was once a belief that the approx. number of islands was about 365....

 and Cliff Island

Cliff Island, Maine

Cliff Island is an island in Casco Bay Maine. It is part of the city of Portland, Maine. As of the 2000 census, the island had a year-round population of approximately 60 people. In the summer, the island's population grows to about 200, despite the fact that it is the only year-round inhabited...

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The company has a fleet of five vessels. Schedules to the islands vary seasonally. During the summer months, many more ferry trips go back and forth to the islands, while there are significantly fewer trips during the winter.
The Casco Bay Steamboat Company began proving permanent year-round service to Casco Bay Islands in 1878.