The U.S. state of Connecticut began as three distinct settlements of Puritans from Massachusetts and England; they combined under a single royal charter in 1663. Known as the "land of steady habits" for its political, social and religious conservatism, the colony prospered from the trade and farming of its ethnic English Protestant population. The Congregational and Unitarian churches became prominent here. Connecticut played an active role in the American Revolution, and became a bastion of the conservative, business-oriented, Constitutionalism Federalist Party.

The word "Connecticut" is a French corruption of the Algonkian word quinetucket, which means "beside the long, tidal river".

Reverend Thomas Hooker and John Haynes led a group of about 100 who, in 1636, founded the settlement of Hartford, named for Samuel Stone's place of birth: Hertford, in England. Called today "the Father of Connecticut," Thomas Hooker was a towering figure in the early development of colonial New England. He was one of the great preachers of his time, an erudite writer on Christian subjects, the first minister of Cambridge, Massachusetts, one of the first settlers and founders of both the city of Hartford and the state of Connecticut, and cited by many as the inspiration for the "Fundamental Orders of Connecticut," cited by some as the world's first written democratic constitution that established a representative government.

The state took a leading role in the Industrial Revolution of the United States, with its many factories establishing a worldwide reputation for advanced machinery. The educational and intellectual establishment was strongly led by Yale College, by scholars such as Noah Webster and by writers such as Mark Twain, who lived in Connecticut after establishing his association with the Mississippi River. Many Yankees left the farms to migrate west to New York and the Midwest in the early nineteenth century. Meanwhile, the heavy demand for labor in the nineteenth century attracted Irish, English and Italian immigrants, among many others, to the medium and small industrial cities. In the early 20th century, immigrants came from eastern and southern Europe. While the state produced few nationally prominent political leaders, Connecticut has usually been a swing state closely balanced between the parties. In the 21st century, the state is known for production of jet engines, nuclear submarines, and advanced pharmaceuticals.

The name Connecticut is derived from the Mohegan-Pequot word that has been translated as "long tidal river" and "upon the long river", referring to the Connecticut River. Evidence of human presence in the Connecticut region dates to as much as 10,000 years ago. Stone tools were used for hunting, fishing, and woodworking. Semi-nomadic in lifestyle, these peoples moved seasonally to take advantage of various resources in the area. They shared languages based on Algonquian. The Connecticut region was inhabited by multiple Indian tribes which can be grouped into the Nipmuc, the Sequin or "River Indians" (which included the Tunxis, Schaghticoke, Podunk, Wangunk, Hammonassett, and Quinnipiac), the Mattabesec or "Wappinger Confederacy" and the Pequot-Mohegan. Some of these groups continue to abide in Connecticut, including the Mohegans, the Pequots, and the Paugusetts.

Various Algonquian tribes long inhabited the area prior to European settlement. The Dutch were the first Europeans in Connecticut. In 1614 Adriaen Block explored the coast of Long Island Sound, and sailed up the Connecticut River at least as far as the confluence of the Park River, site of modern Hartford. By 1623, the new Dutch West India Company regularly traded for furs there and ten years later they fortified it for protection from the Pequot Indians, as well as from the expanding English colonies. The site was named "House of Hope" (also identified as "Fort Hoop", "Good Hope" and "Hope"), but encroaching English colonists made them agree to withdraw in the 1650 Treaty of Hartford. By 1654 they were gone, before the English took over New Netherland in 1664.

The first English colonists came from the Bay Colony and Plymouth Colony in Massachusetts. Original Connecticut Colony settlements were at Windsor in 1633; at Wethersfield in 1634; and in 1636, at Hartford and Springfield, (the latter was administered by Connecticut until defecting in 1640.) The Hartford settlement was led by Reverend Thomas Hooker.

In 1631, the Earl of Warwick granted a patent to a company of investors headed by William Fiennes, 1st Viscount Saye and Sele, and Robert Greville, 2nd Baron Brooke. They funded the establishment of the Saybrook Colony (named for the two lords) at the mouth of the Connecticut River, where Fort Saybrook, was erected in 1636. Another Puritan group left Massachusetts and started the New Haven Colony farther west on the northern shore of Long Island Sound in 1637. The Massachusetts colonies did not seek to govern their progeny in Connecticut and Rhode Island. Communication and travel were too difficult, and it was also convenient to have a place for nonconformists to go.