Prior to British colonization, the Connecticut River valley was populated by bands of the Western Abenaki, who lived in sometimes-large villages of longhouses. Depending on the season, they would either remain near their villages to fish, gather plants, engage in sugaring, and trade or fight with their neighbors, or head to nearby fowling and hunting grounds. Later, they also farmed tobacco and the "three sisters": corn, beans, and squash.
In the 1790 census, the town had 538 residents. Unity was on the Second New Hampshire Turnpike, an important trade route chartered in 1799 that connected Amherst, New Hampshire to Claremont. By 1810, the town had 1,044 inhabitants, with two grain mills, five sawmills, a clothing mill and a distillery. Sheep farming was a principal business.
2008 presidential politics
On June 27, 2008, Presidential candidate Barack Obama and former rival Hillary Rodham Clinton appeared together in Unity at their first public event since Clinton pulled out of the race to be the Democratic presidential candidate. Unity was reportedly chosen because of the town's name and because, in the 2008 primary, Obama and Clinton each received 107 votes from Unity citizens.