Merrimack is a town in Hillsborough County, New Hampshire, United States. The population was 25,494 at the 2010 census, making it the eighth-largest municipality in New Hampshire. In 2013, Merrimack was named the twenty-third best place to live in the United States by CNN Money Magazine.There are four villages in the town: Merrimack Village, Thorntons Ferry, Reeds Ferry, and South Merrimack.