Before Europeans arrived, the New Haven area was the home of the Quinnipiac tribe of Native Americans, who lived in villages around the harbor and subsisted off local fisheries and the farming of maize. After the signing of a treaty in 1638, the Quinnipiac became the first of the indigenous peoples to be placed on a reservation by the English. Later treaties resulted in additional reservations at Branford, Madison, Derby, and Farmington.

A year after its founding by English Puritans in 1638, eight streets were laid out in a four-by-four grid, creating what is commonly known as the "Nine Square Plan". The central common block is the New Haven Green, a 16-acre square at the center of Downtown New Haven. The Green is now a National Historic Landmark, and the "Nine Square Plan" is recognized by the American Planning Association as a National Planning Landmark.

Hillhouse Avenue is famous for its many nineteenth century mansions. Because of the nature of the street, its lots, and its orientation to the nine-square-grid of New Haven (the nation's first planned city), Hillhouse Avenue is sometimes considered to be the first suburb in the United States.

Founded in 1701 as the Collegiate School, Yale University is the third-oldest institution of higher education in the United States and among the most prestigious in the world. As New Haven's biggest taxpayer and employer, the university also serves as an integral part of the city's economy.

New Haven had the first public tree planting program in America, producing a canopy of mature trees (including some large elms) that earned the city its nickname: "The Elm City".

Lollypops were invented by George Smith of New Haven, Connecticut, who started making large hard candies mounted on sticks in 1908. He named them after a racehorse of the time, Lolly Pop, and trademarked the lollipop name in 1931.

New Haven is the birthplace of former president George W. Bush, who was born when his father, former president George H. W. Bush, was living in New Haven while a student at Yale. In addition to being the site of the college educations of both Presidents Bush, New Haven was also the temporary home of former presidents William Howard Taft, Gerald Ford, and Bill Clinton.

As one of the original 13 colonies, Connecticut has no shortage of ghost stories, but one of the most popular is the legend of Mary Hart, who was supposedly buried alive in 1872. When her Aunt forced the townspeople to dig up the coffin and reopen it, they found that Mary's fingernails were bloody, and the inside of the coffin had multiple scratch marks. According to local legend, Midnight Mary still wanders the cemetery at night, and her gravestone warns that anyone who visits her grave at midnight "shall be troubled and pass away."

Roger Sherman is the only person to have signed all four great state papers of the United States: the Continental Association, the Declaration of Independence, the Articles of Confederation, and the Constitution. He was elected Mayor of New Haven in 1784 and held the office until his death.

The Knights of Columbus were founded in New Haven in 1882. The city still serves as the world headquarters of the organization, which maintains a museum downtown.