Penobscot Bay (French: Baie de Penobscot) is an inlet of the Gulf of Maine and Atlantic Ocean in south central Maine. The bay originates from the mouth of Maine's Penobscot River, downriver from Belfast. Penobscot Bay has many working waterfronts including Rockland, Rockport, and Stonington, and Belfast upriver. Penobscot Bay is between Muscongus Bay and Blue Hill Bay, just west of Acadia National Park. 11,000 years ago, at the beginning of the Holocene epoch, the Gulf of Maine's sea level fell as low as 180 feet (55 m) below its present height. Penobscot Bay was then a continuation of Penobscot River that meandered through a broad lowland extending past present day Matinicus Island.Penobscot Bay and its chief tributary, Penobscot River are named for the Penobscot Indian Nation, which has continuously inhabited the area for more than ten thousand years, fishing, hunting and shellfish gathering in and around the bay and river. A part of the Wabanaki Confederacy, the Penobscot Indian Nation's present reservation includes Indian Island, north of Orono, Maine, and all the islands of Penobscot River above it. Ancient remains of their campsites dating back millennia have been found on the bay's shores and islands. The bay was the site of a humiliating American defeat during the Revolutionary War. A Continental Navy flotilla consisting of 19 warships and 25 support vessels was dispatched on July 24 to recapture the mid-coast of Maine from the British who had captured part of the territory and constructed fortifications near the bay, naming the newly captured territory New Ireland. The American besiegers became stalled in their assaults due to dissension between Solomon Lovell and Dudley Saltonstall, two of the expeditions commanders, and after a British flotilla led by George Collier arrived on August 13, the American fleet fled, beaching and burning their ships in the face of a superior British force. All 44 ships were either destroyed or captured, in what proved to be America's worst naval defeat until Pearl Harbor, 162 years later.There are many islands in this bay, and on them, some of the country's most well-known summer colonies.

Belfast is a city in Waldo County, Maine, in the United States. As of the 2010 census, the city population was 6,668. Located at the mouth of the Passagassawakeag River estuary on Belfast Bay and Penobscot Bay. Belfast is the county seat of Waldo County. Its seaport has a wealth of antique architecture in several historic districts, and remains popular with tourists.

Bangor () is a city in the U.S. state of Maine and the county seat of Penobscot County. The city proper has a population of 33,039, making it the state's 3rd-largest settlement, behind Portland (66,882) and Lewiston (36,221). Modern Bangor was established in the mid-19th century with the lumber and shipbuilding industries. Lying on the Penobscot River, logs could be floated downstream from the Maine North Woods and processed at the city's water-powered sawmills, then shipped from Bangor's port to the Atlantic Ocean 30 miles (48 km) downstream, and from there to any port in the world. Evidence of this is still visible in the lumber barons' elaborate Greek Revival and Victorian mansions and the 31-foot-high (9.4 m) statue of Paul Bunyan. Today, Bangor's economy is based on services and retail, healthcare, and education. Bangor has a port of entry at Bangor International Airport, also home to the Bangor Air National Guard Base. Historically Bangor was an important stopover on the great circle route air route between the U.S. East Coast and Europe. Bangor has a humid continental climate, with cold, snowy winters, and warm summers.

Camden is a town in Knox County, Maine, United States. The population was 4,850 at the 2010 census. The population of the town more than triples during the summer months, due to tourists and summer residents. Camden is a summer colony in the Mid-Coast region of Maine. Similar to Bar Harbor, Nantucket and North Haven, Camden is well known for its summer community of wealthy Northeasterners, mostly from Boston, New York and Philadelphia.