Brentwood is a town in Rockingham County, New Hampshire. It is the county seat of Rockingham County, and its population at the 2010 census was 4,486. The Piscassic, Little and Exeter rivers drain the area covered by the town.
While lumber production did occur towards the beginning of the establishment of the town, it later became predominantly agricultural. Now, it is a residential community. Commercial activities include sales, contruction, production and transport of materials, management and finance, and professional services.