New Boston is a town in Hillsborough County, New Hampshire, United States. The population was 6,108 at the 2020 census, up from 5,321 at the 2010 census. New Boston is home to the annual Hillsborough County Agricultural Fair and the Molly Stark Cannon. The 1743 cannon, which appears on the town seal, was given by General John Stark to the New Boston Artillery Company after the Battle of Bennington.

Hillsborough County is the most populous county in the U.S. state of New Hampshire. As of the 2020 census, the population was 422,937, almost one-third the population of the entire state. Its county seats are Manchester and Nashua, the state's two biggest cities. Hillsborough is northern New England's most populous county as well as its most densely populated.