Mont Vernon is a town in Hillsborough County, New Hampshire, United States. Mont Vernon broke away from neighboring Amherst in 1803, following a dispute over the town parish. It later added a small portion of neighboring Lyndeborough. Mont Vernon's general history follows that of many towns in this region: Originally settled for agriculture, its farms were hard hit after the Civil War when railroads opened up better farming land in the Midwest. Population peaked in 1870 and began to decline.