Derry is a town in Rockingham County, New Hampshire, United States. The population was 34,317 at the 2020 census. Although it is a town and not a city, Derry is the most populous community in Rockingham County and the 4th most populous in the state. The town's nickname, "Spacetown", derives from the fact that Derry is the birthplace of Alan Shepard, the first astronaut from the United States in space. Derry was also for a time the home of the poet Robert Frost and his family.

The town is the basic unit of local government and local division of state authority in the six New England states. Most other U.S. states lack a direct counterpart to the New England town. New England towns overlay the entire area of a state, similar to civil townships in other states where they exist, but they are fully functioning municipal corporations, possessing powers similar to cities and counties in other states. New Jersey's system of equally powerful townships, boroughs, towns, and cities is the system which is most similar to that of New England. New England towns are often governed by a town meeting, an assembly of eligible town residents. The great majority of municipal corporations in New England are based on the town model; there, statutory forms based on the concept of a compact populated place are uncommon, though elsewhere in the U.S. they are prevalent. County government in New England states is typically weak at best, and in some states nonexistent. Connecticut, for example, has no county governments, nor does Rhode Island. Both of those states retain counties only as geographic subdivisions with no governmental authority, while Massachusetts has abolished eight of fourteen county governments so far. Counties serve mostly as dividing lines for the states' judicial systems and some other state services in the southern New England states, while providing varying services in the more sparsely populated three northern New England states.