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. There are four villages in the town: Merrimack Village (formerly known as Souhegan Village), Thornton's Ferry, Reed's Ferry, and South Merrimack. Human beings began to settle the area currently known as Merrimack sometime after the recession of the glaciers that had spread over much of New England during the last ice age. European settlers first came to the area in the late 17th century when the area was still in dispute between the Province of New Hampshire and Massachusetts Bay Colony.