Dorchester (colloquially referred to as Dot) is a Boston neighborhood comprising more than 6 square miles (16 km2) in the City of Boston, Massachusetts, United States. Originally, Dorchester was a separate town, founded by Puritans who emigrated in 1630 from Dorchester, Dorset, England to the Massachusetts Bay Colony. This dissolved municipality, Boston's largest neighborhood by far, is often divided by city planners in order to create two planning areas roughly equivalent in size and population to other Boston neighborhoods.
The neighborhood is named after the town of Dorchester in the English county of Dorset, from which Puritans emigrated on the ship Mary and John, among others.
Founded in 1630, just a few months before the founding of the city of Boston, Dorchester now covers a geographic area approximately equivalent to nearby Cambridge. It was still a primarily rural town and had a population of 12,000 when it was annexed to Boston in 1870. Railroad and streetcar lines brought rapid growth, increasing the population to 150,000 by 1920. In the 2010 United States Census, the neighborhood's population was 92,115.
The Dorchester neighborhood has a very diverse population, which includes a large concentration of African Americans, European Americans (with large Irish American and Polish American immigrant populations), Caribbean Americans, Latinos, and East and Southeast Asian Americans. Dorchester also has a significant LGBT population, with active political groups and the largest concentration of same-sex couples in Boston after the South End and Jamaica Plain. Most of the people over the age of 25 have completed high school or obtained a GED.