The indigenous Wampanoag inhabited the area that is now Dartmouth for up to a thousand years before European colonization, and their ancestors had been there longer. English colonist Bartholomew Gosnold is recorded as having explored this area, later developed as Old Dartmouth, in 1602. Elders of the Plymouth Colony purchased the territory of Old Dartmouth from Wampanoag chiefs Massasoit and Wamsutta around March 7, 1652 for “30 yards of cloth, eight moose skins, fifteen axes, fifteen hoes, fifteen pair of breeches, eight blankets, two kettles, one cloak, £2 in wampum, eight pair stockings, eight pair shoes, one iron pot and 10 shillings in another commoditie .”

Dartmouth was settled by English immigrants around November 1652, and it was officially incorporated in 1664. In its early centuries, Dartmouth developed as an agricultural and seafaring community. During the late 19th century its coastline became a summer resort area for wealthy members of New England society.

It was named for the town of Dartmouth, Devon, England, from where the Puritans originally intended to depart for America. The Puritans sold the town to the Religious Society of Friends or Quakers, who wished to live outside the stringent religious laws of the Puritans in Plymouth.

There are still Quaker meeting houses in town, including the Smith Neck Meeting House, the Allens Neck Meeting House, and the Apponegansett Meeting House, which is on the National Register of Historic Places. The town’s borders were originally named in the charter (and set by King Philip) as the lands of “Acushnea, Ponagansett, and Coaksett.” This includes the land of the towns of Westport, Fairhaven, and Acushnet, and the city of New Bedford. In 1789, the towns of Westport and New Bedford, which included Fairhaven and Acushnet, separated and were incorporated as towns themselves.

The Lloyd Center for Environmental Studies, located in South Dartmouth, is a non-profit organization that provides educational programs on aquatic environments in southeastern New England. It is across the mouth of the Slocums River from Demarest Lloyd State Park, a popular state beach known for its shallow waters.

The Dartmouth Natural Resource Trust in South Dartmouth, holds over 1,500 conserved acres of land. The property has 35 miles of hiking trails, and ocean and river walks. The Trust organizes such activities as photography tours, summer outdoor yoga series, bird watching, and plant identification. Its summer evening Barn Bash and winter fundraising auction are held annually.

Round Hill was the site of early-to-mid 20th century research into the uses of radio and microwaves for aviation and communication by MIT scientists, including physicist Robert J. Van de Graaff. There in 1933 he built the world’s largest air-insulated Van de Graaff generator (now located at the Museum of Science (Boston)). It is also the site of the Green Mansion, the estate of “Colonel” Edward Howland Robinson Green, a colorful character who was son of the even more colorful and wildly eccentric Hetty Green, nicknamed the “Witch of Wall Street”. Hetty was said to be the richest woman in the world in her time, and is listed in the Guinness Book of Records as the “world’s greatest miser.”

In 1936, the Colonel died. The estate fell into disrepair as litigation over his vast fortune continued for eight years between his widow and his sister. Finally, the court ruled that Mrs. Hetty Sylvia Wilks, the Colonel’s sister, was the sole beneficiary. In 1948, she bequeathed the entire estate to MIT, which used it for microwave and laser experiments. The giant antenna, which was a landmark to sailors on Buzzards Bay, was erected on top of a 50,000-gallon water tank. Although efforts were made to preserve the structure, it deteriorated and was demolished on November 19, 2007.

Another antenna was erected next to the mansion and used in the development of the Ballistic Missile Early Warning System. MIT continued to use Round Hill through 1964. It was sold to the Society of Jesus of New England and was used as a retreat house. The upper floors were divided into 64 individual rooms. The main floor was fitted with a chapel, a library, and meeting rooms.

In 1970 the Jesuits sold the land and buildings to Gratia R. Montgomery. In 1981, Mrs. Montgomery sold most of the land to a group of developers who have worked to preserve the history, grandeur and natural environment. The property is now a gated, mostly summer residential community on the water featuring a nine-hole golf course.

According to the United States Census Bureau, the town has a total area of 97.5 square miles (252.6 km²). 60.9 square miles (157.8 km²) of it is land and 94.8 square kilometres (36.6 sq mi) of it, 37.53%, is water. It is the third largest town by area in Massachusetts.

The town is accessible by Interstate 195 and U.S. Route 6, which run parallel to each other through the northern-main business part town from New Bedford to Westport on an east-west axis within a mile or two apart from one another.

Dartmouth includes the Southeastern Massachusetts Bioreserve that extends from Fall River into many protected forests of North Dartmouth in the Collins Corner, Faunce Corner, and Hixville sections of town. The Southeastern Massachusetts Bioreserve actually extends its protected forest lands into the Freetown-Fall River State Forest and beyond.

There are many rivers that flow north-south in Dartmouth, such as the Copicut River, Shingle Island River, Paskamanset River, Slocums River, Destruction Brook, and Little River. Dartmouth is divided into two primary sections: North Dartmouth (USPS ZIP code 02747) and South Dartmouth (USPS ZIP code 02748).

The town is bordered by Westport to the west, New Bedford to the east, Fall River to the north, and Buzzards Bay/the Atlantic Ocean to the south.

The highest point in the town is near its northwest corner, where the elevation rises to over 256 feet (78 m) above sea level north of Old Fall River Road.

Dartmouth is located in the Ninth Bristol state representative district, which includes all of Dartmouth as well as parts of Freetown, Lakeville, and New Bedford. The current state representative is Christopher Markey. The town is represented by Mark Montigny in the state senate in the Second Bristol and Plymouth district, which includes the city of New Bedford and the towns of Acushnet, Dartmouth, Fairhaven, and Mattapoisett. Dartmouth is the home of the Third Barracks of Troop D of the Massachusetts State Police, which recently^[when?] relocated from Route 6 to just north of the retail center of town along Faunce Corner Road. On the national level, the town is part of Massachusetts Congressional District 9, which is represented by William R. Keating. The state’s junior (Class I) Senator is Ed Markey and the state’s senior (Class II) Senator, is Elizabeth Warren.

Dartmouth is governed by a representative town meeting form of government, led by the Select Board. The Town Hall is located in the former Poole School, which also served as Dartmouth High School for several years. The town is patrolled by a central police department, located in the former Town Hall near the village of Padanaram. There are five fire stations in the town divided among three fire districts, all of which are paid-call departments. There are two post offices (North Dartmouth, under the 02747 zip code, and South Dartmouth, under the 02748 zip code).

The Bristol County Sheriff’s Office maintains its administrative headquarters and operates several jail facilities in the Dartmouth Complex in North Dartmouth in Dartmouth. Jail facilities in the Dartmouth Complex include the Bristol County House Of Correction and Jail, the Bristol County Sheriff’s Office Women’s Center, and the C. Carlos Carreiro Immigration Detention Center.

Massachusetts Route 140 and Massachusetts Route 24 are located just outside Dartmouth’s borders in New Bedford and Fall River, respectively, and both provide access to Boston and points north of the area. Massachusetts Route 177 begins just over Dartmouth’s border with Westport, running west into Rhode Island and providing a link between the Newport-area (Tiverton, Little Compton, and Aquidneck Island) with the Fall River/New Bedford area. Interstate 195 and US Route 6 pass directly through Dartmouth, and also offer connections to the aforementioned three Massachusetts routes; the former provides access to Route 140, while the latter can be used to access Route 24 and Route 177.

Both Tiverton, RI and Little Compton, RI are geographically part of Massachusetts, lacking direct interstate highway connections with the rest of Rhode Island. Instead, smaller routes connect to the area (RI 138, MA/RI 24, RI 177/MA 177, and MA 81, and MA 88).^{[clarification needed]} Route 24 lies an average of 15 to 20 miles away in Tiverton, RI and Little Compton, RI, Massachusetts Route 177 and Massachusetts Route 140 and Massachusetts Route 24 are based upon old Indian routes and trails.

Public transportation in Dartmouth is primarily provided by the Southeastern Regional Transit Authority, which provides direct bus services between several points in Dartmouth and to the adjacent cities of New Bedford and Fall River. Transfers at either termini offer connections to T.F. Green Airport via Plymouth & Brockton Street Railway and various locales in Rhode Island via Peter Pan Bus; the latter company also offers connections from New Bedford to Cape Cod and Boston. Direct daily bus service from University of Massachusetts Dartmouth to Taunton and Boston is also offered via DATTCO buses.

Despite its border along Buzzard’s Bay, Dartmouth does not have any major water-based transport. However, the adjacent cities of Fall River and New Bedford offer several indirect ferry connections, with routes to Newport and Block Island from the former and Martha’s Vineyard, Nantucket, and Cuttyhunk from the latter.

While Dartmouth and neighboring communities currently do not have any rail connections, construction of MBTA commuter rail stations is currently underway in Fall River and New Bedford as part of the South Coast Rail project. Upon completion, these will offer railway connections to cities including Taunton, Brockton, Braintree, and Boston.

A small segment of railway, known as the Watuppa branch, passes through Dartmouth before terminating in the nearby town of Westport. The primary operator of freight rail in Dartmouth is Bay Colony Railroad, which operates along the Watuppa branch and interchanges with CSX in New Bedford.