Dorchester was originally inhabited by the Neponset/Neponsett tribe of the Massachusett nation. For generations, they made their home along the Neponset River estuary, which was a plentiful source of food due to the freshwater meeting the salt water. The Neponsett “concept of land ownership differed sharply from the European. The Massachusett did not own the land, but what was on it or what it produced. The Neponsett owned the shellfish beds, beaver, and trout from the marsh and river; the planting fields from the hillsides and the deer from the forests.”

As one of the first groups of Indigenous peoples to encounter English colonists, the Neponset people experienced a rapid decline in population in the 17th and 18th centuries due to violence perpetrated by the English and infectious diseases brought by the Europeans. The Massachusett leader, Chickatawbut, negotiated with the first settlers, but he died of smallpox in 1633, and his brother, Cutshamekin deeded further land to the settlers. Despite several centuries of struggle due to European settlement, members of the Neponsett/Ponkapoag tribe continue to live in the Boston area and have established a tribal council.

In 1626 David Thompson settled his family on Thompson Island in what is now Dorchester before Boston’s Puritan migration wave began in 1630. May 30, 1630, Captain Squib of the ship Mary and John entered Boston Harbor and on June 17, 1630, landed a boat with eight men on the Dorchester shore, at what was then a narrow peninsula known as Mattapan or Mattaponnock, and today is known as Columbia Point (more popularly since 1984 as Harbor Point). Those aboard the ship who founded the town included William Phelps, Roger Ludlowe, John Mason, John Maverick, Nicholas Upsall, Capt. Roger Fyler, William Gaylord, Henry Wolcott and other men who would become prominent in the founding of a new nation. The original settlement founded in 1630 was at what is now the intersection of Columbia Road and Massachusetts Avenue. (Even though Dorchester was annexed over 100 years ago into the city of Boston, this founding is still celebrated every year on Dorchester Day, which includes festivities and a parade down Dorchester Avenue).

Most of the early Dorchester settlers came from the West Country of England, and some from Dorchester, Dorset, where the Rev. John White was chief proponent of a Puritan settlement in the New World. (Rev. John White has been referred to as the unheralded champion of the Massachusetts Bay Colony, because despite his heroic efforts on its behalf, he remained in England and never emigrated to the Colony he championed.) The town that was founded was centered on the First Parish Church of Dorchester, which still exists as the Unitarian-Universalist church on Meeting House Hill and is the oldest religious organization in present-day Boston.

On October 8, 1633, the first Town Meeting in America was held in Dorchester. Today, each October 8 is celebrated as Town Meeting Day in Massachusetts. Dorchester is the birthplace of the first public elementary school in America, the Mather School, established in 1639. The school still stands as the oldest elementary school in America. In 1634 Israel Stoughton built one of the earliest grist mills in America on the Neponset River, and Richard Callicott founded a trading post nearby. In 1641, Dorcas ye blackmore, a servant to Israel Stoughton, was the first recorded African American to join a church in New England, and she served as an evangelist to Stoughton’s Native American servants, and the First Parish Church of Dorchester attempted to help Dorcas gain her freedom.

In 1649, Puritan missionaries, including John Eliot, began a campaign to convert the Indigenous people in Dorchester to Christianity with the help of Cockenoe and John Sassamon, two Indian servants in Dorchester. Eliot was given land by the town of Dorchester for his mission, where he established a church and school.

The oldest surviving home in the city of Boston, the James Blake House, is located at Edward Everett Square, which is the historic intersection of Columbia Road, Boston Street, and Massachusetts Avenue, a few blocks from the Dorchester Historical Society. The Blake House was constructed in 1661, as was confirmed by dendrochronology in 2007.

In 1695, a party was dispatched to found the town of Dorchester, South Carolina, which lasted barely a half-century before being abandoned.

In 1765, chocolate was first introduced in the American colonies when Irish chocolate maker John Hannon (or alternatively spelled “Hannan” in some sources) imported beans from the West Indies and refined them in Dorchester, working with Dr. James Baker, an American physician and investor. They soon after opened America’s first chocolate mill and factory in the Lower Mills section of Dorchester. The Walter Baker Chocolate Factory, part of Walter Baker & Company, operated until 1965.^:627

Before the American Revolution, “The Sons of Liberty met in August 1769 at the Lemuel Robinson Tavern, which stood on the east side of the upper road (Washington St.) near the present Fuller Street. Lemuel Robinson was a representative of the town during the Revolution and was appointed a colonel in the Revolutionary army.” Dorchester (in a part of what is now South Boston) was also the site of the Battle of Dorchester Heights in 1776, which eventually resulted in the British evacuating Boston.

In Victorian times, Dorchester became a popular country retreat for Boston elite, and developed into a bedroom community, easily accessible to the city—a streetcar suburb. The mother and grandparents of John F. Kennedy lived in the Ashmont Hill neighborhood while John F. “Honey Fitz” Fitzgerald was mayor of Boston.

The American poet Oliver Wendell Holmes, wrote a poem called “The Dorchester Giant” in 1830, and referred to the special kind of stone, “Roxbury puddingstone”, also quarried in Dorchester, which was used to build churches in the Boston area, most notably the Central Congregational Church (later called the Church of the Covenant) in Boston’s Back Bay neighborhood.

In 1845, the Old Colony Railroad ran through the area and connected Boston and Plymouth, Massachusetts. The station was originally called Crescent Avenue or Crescent Avenue Depot as an Old Colony Railroad station, then called Columbia until December 1, 1982, and then again changed to JFK/UMASS. It is a Massachusetts Bay Transportation Authority rail line station for both the Red Line subway and the Plymouth/Kingston, Middleborough/Lakeville and Greenbush commuter rail lines.

In the 1840s and 1850s, a new wave of development took place on a strip of waterfront overlooking Dorchester Bay (Park and Mill Streets at the Harrison Square Historic District, later known as Clam Point.) Renowned architects who had contributed to one of the most significant and intact collections of Clam Point’s Italianate mansards include Luther Briggs, John A. Fox, and Mary E. Noyes. By the 1890s, Clam Point gained prominence as a summer resort with the Russell House hotel as its centerpiece and the establishment of the Dorchester Yacht Club on Freeport Street.

In the 1880s, the calf pasture on Columbia Point was used as a Boston sewer line and pumping station. This large pumping station still stands and in its time was a model for treating sewage and helping to promote cleaner and healthier urban living conditions. It pumped waste to a remote treatment facility on Moon Island in Boston Harbor, and served as a model for other systems worldwide. This system remained in active use and was the Boston Sewer system’s headworks, handling all of the city’s sewage, until 1968 when a new treatment facility was built on Deer Island. The pumping station is also architecturally significant as a Richardsonian Romanesque designed by the then Boston city architect, George Clough. It is also the only remaining 19th century building on Columbia Point and is in the National Register of Historic Places.

Dorchester was annexed by Boston in pieces beginning on March 6, 1804, and ending with complete annexation to the city of Boston after a plebiscite was held in Boston and Dorchester on June 22, 1869. As a result, Dorchester officially became part of Boston on January 3, 1870. This is also the historic reason that Dorchester Heights is today considered part of South Boston, not modern-day Dorchester, since it was part of the cession of Dorchester to Boston in 1804. Additional parts of Dorchester were ceded to Quincy (in 1792, 1814, 1819, and 1855) and portions of the original town of Dorchester became the separate towns of Hyde Park (1868 and later annexed to Boston in 1912), Milton (1662), and Stoughton (1726, itself later subdivided).

In 1895, Frederick Law Olmsted, architect of the Boston Public Garden/Emerald Necklace and Central Park, was commissioned to create Dorchester Park, to be an urban forest for the residents of a growing Dorchester.

In 1904, the Dorchester Historical Society incorporated “Dorchester Day” which commemorated the settlement of Dorchester in 1630. An annual event, Dorchester Day is a tableau of community events, highlighted by such activities as the Landing Day Observance, the Dorchester Day Parade along Dorchester Avenue the first Sunday in June, and as a grand finale, the Community Banquet.

There was also increased social activism in Dorchester during the late 19th and early 20th centuries. Dorchester became home to the first racially integrated neighborhood, on Jones Hill. One of the residents of that neighborhood, William Monroe Trotter, with W.E.B. Du Bois, helped to found the Niagara Movement, the precursor of the National Association for the Advancement of Colored People. Many leading suffragettes also lived in Dorchester, including Lucy Stone.

In the early 20th century, Dorchester also saw a large influx of new immigrants from origins such as Ireland, French Canada, Poland, Italy, and migrant African Americans from the south. This is the era when the trademark Dorchester triple decker apartment buildings were built.^{[citation needed]}

In the early 1950s, Dorchester was also a center of civil rights activism. Martin Luther King Jr. lived there for much of the time he attended Boston University for his PhD. “With Boston’s Baptist community riveted by his preaching and Coretta [Scott King] at his side, King’s circle grew. The Dorchester apartment drew friends and followers like a magnet, according to [friend and roommate John] Bustamante, with ‘untold numbers of visitors coming from the other schools.’ The roommates housed and fed the visitors, who would join in civil rights discussions.”

During the 1960s–1980s, the ethnic landscape of Dorchester changed dramatically. The Jewish, Italian, and Irish populations were replaced with African, Asian, and Caribbean populations.

The first community health center in the United States was the Columbia Point Health Center in Dorchester. It was opened in December 1965 and served mostly the massive Columbia Point public housing complex adjoining it. It was founded by two medical doctors, Jack Geiger who had been on the faculty of Harvard University then later at Tufts University and Count Gibson from Tufts University. Geiger had previously studied the first community health centers and the principles of Community Oriented Primary Care with Sidney Kark and colleagues while serving as a medical student in rural Natal, South Africa. The Columbia Point Health Center is still in operation and was rededicated in 1990 as the Geiger-Gibson Community Health Center.

In 1974, the University of Massachusetts Boston moved from Park Square in downtown Boston to the Columbia Point in Dorchester. In 1982, Boston State College was incorporated into UMass Boston. Since the 1970s, UMass Boston has expanded substantially, including building a new campus center in 2004 and a new science center in 2015. It has also hosted numerous important social and civic events. In 2000, for example, the university hosted a presidential candidates’ debate between George W. Bush and Al Gore.

In 1977, after an unsuccessful bid to have the John F. Kennedy Library in Cambridge, Massachusetts, close to Harvard University, ground was broken at the tip of Columbia Point for the John F. Kennedy Presidential Library and Museum, designed by the architect I. M. Pei, and dedicated on October 20, 1979.

By the 1980s, the Blue Hill Avenue section of Dorchester had become a predominantly Black community.

During the 1990s, the city administration increased police presence and invested city money into the area for more street lighting.^{[citation needed]}

On March 30, 2015, the Edward M. Kennedy Institute for the United States Senate was dedicated by President Barack Obama. The Institute opened to the public on March 31, 2015.

Dorchester is located south of downtown Boston and is surrounded by the neighborhoods of South Boston, Roxbury, Jamaica Plain, Hyde Park, South End, and the city of Quincy and town of Milton. The Neponset River separates Dorchester from Quincy and Milton. According to the U.S. Postal Service, Dorchester includes the zip codes 02121, 02122, 02124, and 02125.

Dorchester is Boston’s largest and most populous neighborhood and comprises many smaller sections and squares. Due to its size of about six square miles, it is often divided for statistical purposes in North and South Dorchester. North Dorchester includes the portion north of Quincy Street, East Street and Freeport Street. The main business district in this part of Dorchester is Uphams Corner, at the intersection of Dudley Street and Columbia Road. South Dorchester is bordered to the east by Dorchester Bay and to the south by the Neponset River. The main business districts in this part of Dorchester are Fields Corner, at the intersection of Dorchester Avenue and Adams Street, and Codman Square, at the intersection of Washington Street and Talbot Avenue. Adjacent to Fields Corner is the Harrison Square Historic District, also known as Clam Point, noteworthy for its collection of substantial Italianate Mansard residences.

Dorchester Avenue is the major neighborhood spine, running in a south-north line through all of Dorchester from Lower Mills to downtown Boston. The southern part of Dorchester is primarily a residential area, with established neighborhoods still defined by parishes, and occupied by families for generations. The northern part of Dorchester is more urban, with a greater amount of apartment housing and industrial parks. South Bay and Newmarket industrial area are major sources of employment and the Harbor Point area (formerly known as Columbia Point) is home of several large employers, including the Boston campus of the University of Massachusetts, the Massachusetts Archives and Commonwealth Museum, the Edward M. Kennedy Institute for the United States Senate, and the John F. Kennedy Presidential Library and Museum. Distinct commercial districts include Bowdoin/Geneva, Fields Corner, Codman Square, Peabody Square, Adams Village and Lower Mills. Primarily residential areas include Savin Hill, Jones Hill, Four Corners, Franklin Field, Franklin Hill, Ashmont, Meeting House Hill, Neponset, Popes Hill and Port Norfolk.

Up until the 1960s, the Blue Hill Avenue part of Dorchester from Roxbury to Mattapan was primarily composed of Jewish Americans who had lived there for generations. The Neponset neighborhood was primarily Irish-American. During the 1920s–1960s, many African-Americans moved from the South to the North during the Great Migration and settled on Blue Hill Avenue and nearby sections. While some Jewish-Americans were moving “up and out” to the suburbs, certain Boston banks and real estate companies developed a blockbusting plan for the area. The Blue Hill Avenue area was “redlined” so that only the newly arriving African-Americans would receive mortgages for housing in that section. “White flight” was prevalent. Later, Dorchester had another wave of immigrants, this time from Puerto Rico, the Dominican Republic, Haiti, Jamaica, Trinidad and Tobago, Vietnam, Cape Verde, as well as other Latin American, Asian, and African nations. Dorchester continued to experience immigration from Northern European countries such as Ireland, Germany and Poland. This made Dorchester more diverse than at any point in its long history, and home to more people from more countries than ever before. These immigrants helped revive economically many areas of the neighborhood by opening ethnic stores and restaurants.

The sections of Dorchester have distinct ethnic, racial, and socioeconomic compositions. The eastern areas of Dorchester (especially between Adams Street and Dorchester Bay) are primarily ethnic European and Asian, with a large population of Irish Americans and Vietnamese Americans, while the residents of the western, central and parts of the southern sections of the neighborhood are predominantly African Americans. In Neponset, the southeast corner of the neighborhood, as well as parts of Savin Hill in the north and Cedar Grove in the south, Irish Americans maintain the most visible identity. In the northern section of Dorchester and southwestern section of South Boston is the Polish Triangle, where recent Polish immigrants are residents. Savin Hill, as well as Fields Corner, have large Vietnamese American populations. Uphams Corner contains a Cape Verdean American community, the largest concentration of people of Cape Verdean origin within Boston city limits. Western, central and parts of southern Dorchester have a large Caribbean population (especially people from Haiti, Jamaica, Barbados, and Trinidad and Tobago). They are most heavily represented in the Codman Square, Franklin Field and the Ashmont area, although there are also significant numbers in Four Corners and Fields Corner. Significant numbers of African Americans live in the Harbor Point, Uphams Corner, Fields Corner, Four Corners and Franklin Field areas. In recent years Dorchester has also seen an influx of young residents, gay men and women, and working artists (in areas like Lower Mills, Ashmont Hill/Peabody Square, and Savin Hill).

The American Community Survey (ACS) for Dorchester, from 2007–2011, estimates the total population is 113,975 people. Slightly more than half are female, 52.6% or 59,914 and 47.4% or 54,061 are male.

In Dorchester, 68.4% or 77,980 of the residents are native born and 31.6% or 35,995 people are foreign born, of which 50.1% or 18,024 are not U.S. citizens. The largest racial group in the neighborhood is Black or African-American with 49,612 people or 43.05% of the population. People who self-identify as white represent 26,102 or 26.99% of the community. Hispanic/Latino account for 19.09% of the population with 19,295 resident. The Asian enclave represents 9.6% of 10,990 of the citizenry. The smallest racial group is bi/multi-racial and they make up 1.9% (2,174) of the population.

According to the ACS survey, Dorchester has a large under 25 population with 38.1% or 43,472 people and 33,162 (29.1% of the total population) of them under the age of 19 years old. Between the ages of 25 to 64 years old there are 59,788 or 52.6% people and 10,715 people or 9.3% are over the age of 65 years old. In Dorchester, approximately 61.9% or 70,503 people are over the age of 25, 23.5% or 16,582 people do not have a high school diploma or GED, 30.5% or 21,479 have a diploma or GED, 18.5% or 13,045 people have completed some college, and 27.5% or 19,397 people have a college degree.

The ACS Survey estimates there are 40,443households in the neighborhood of Dorchester, the per capita income of $22,120 and a median income of $44,136. 13.1% or 5,286 households have reported income of less than $10,000. 27.3% or 11,020 households earn less than $19,999. 19.1% or 7,720 households earn between $20,000 to 39,999.16.5% or 6,651 households in the earn between $40,000 to 59,999. 19.7% or 7,977 households earn between $60,000 to 99,999. 15.3% or 6,174 of household report annual incomes of $100,000 to 199,999. Only 2.2% or 901 households in Dorchester earn $200,000 or more per year. The ACS reports as of 2011, Poverty affects 23.5% or 9,511 households and 24.3% or 9,820 of households are receiving SNAP Benefits.

According to the 2012-2016 American Community Survey 5-Year Estimates, the largest ancestry groups in ZIP Codes 02121, 02122, 02124, and 02125 are:

The neighborhood is served by five stations on the Massachusetts Bay Transportation Authority Red Line (MBTA) rapid transit service, five stations on the Ashmont-Mattapan High Speed Line, five stations on the Fairmount Commuter Rail Line, and various bus routes. Over the last decade, the Dorchester branch of the Red Line had major renovations, including four rapid transit stations being rebuilt at Savin Hill, Fields Corner, Shawmut, and Ashmont. At Ashmont station, the city of Boston and the state of Massachusetts partnered with private investors to create The Carruth, one of the state’s first Transit-oriented developments (TOD).

Interstate 93 (concurrent with Route 3 and U.S. 1) runs north–south through Dorchester between Quincy, Massachusetts, and downtown Boston, providing access to the eastern edge of Dorchester at Columbia Road, Morrissey Boulevard (northbound only), Neponset Circle (southbound only), and Granite Avenue (with additional southbound on-ramps at Freeport Street and from Morrissey Blvd at Neponset). Several other state routes traverse the neighborhood, e.g., Route 203, Gallivan Boulevard and Morton Street, and Route 28, Blue Hill Avenue (so named because it leads out of the city to the Blue Hills Reservation). The Neponset River separates Dorchester from Quincy and Milton. The “Dorchester Turnpike” (now “Dorchester Avenue”) stretches from Fort Point Channel (now in South Boston) to Lower Mills, and once boasted a horse-drawn streetcar.

A number of the earliest streets in Dorchester have changed names several times through the centuries, meaning that some names have come and gone. Leavitt Place, for instance, named for one of Dorchester’s earliest settlers, eventually became Brook Court and then Brook Avenue Place. Gallivan Boulevard was once Codman Street and Brookvale Street was once Brook Street.Morrissey Boulevard was once Old Colony Parkway.