Established in 1763, the town was once known as Mast Camp, because it was the shipping point for tall masts floated down the Connecticut River by the English. Incorporated in 1765 by Colonial Governor Benning Wentworth, it was named for Sir Samuel Cornish, a distinguished admiral of the Royal Navy.

Cornish celebrates summer with its annual Cornish Fair, a three-day agricultural fair held on the third weekend in August. In 2007 the Cornish Fair will take place on August 17, 18 and 19 .

Cornish also became a well-known summer resort for artists and writers. Seeking a studio away from the summer heat of New York City, sculptor Augustus Saint-Gaudens began coming to Cornish in 1885. Artist friends followed him, transforming the area into a popular artists' colony. Saint-Gaudens National Historic Site in Cornish is at his former home and studio, and hosts summer concerts as well as ongoing exhibits.

Cornish is the site of the longest wooden covered bridge in the United States, and the longest two-span covered bridge in the world. The Cornish - Windsor Bridge, which spans the Connecticut River, was built in 1866 at an original cost of $9,000.