is a town in Hillsborough County, New Hampshire, United States. The population was 25,119 at the 2000 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.
Merrimack was officially incorporated in 1746, a year largely regarded as Merrimack's birthday, although only the southern portion (primarily what is known as Thornton's Ferry) of the current boundaries of town was included in the original town, with the northern portion of what is now Merrimack (primarily what is known as Reed's Ferry) being added a few years later.
The Boston and Maine Railroad laid tracks through the town in the 19th century, with several stations operating until the mid-20th century when the advent of the automobile transformed Merrimack from a largely agricultural community to a bedroom community of Boston and nearby cities in New Hampshire, becoming one of the northernmost points of the northeastern urban belt sometimes known as Megalopolis. Since 1970 it has been the home of the Anheuser-Busch Brewery, their easternmost plant in the United States, and home to both a brewery tour and one of the five stables for the Budweiser Clydesdales.
The Merrimack School Board attracted national attention in 1995 when it passed a "prohibition of alternative lifestyle instruction" act, which resulted in the removal of a work by William Shakespeare from the school curriculum. The board members who supported the act were voted out in the subsequent board election.