Derry is a town in Rockingham County, New Hampshire, United States. The population was 34,021 at the 2000 census. Although it is a town and not a city, Derry is the fourth most-populous community in New Hampshire. The primary settlement in town, where over 66% of the population resides, is defined by the U.S. Census Bureau as the Derry census-designated place (CDP) and includes the densely-populated portions of the town centered on the intersection of New Hampshire Route 28 and New Hampshire Route 102.