Brentwood is a town in Rockingham County, New Hampshire, United States. As of the 2010 census, the town had a total population of 4,486. Brentwood has been the county seat of Rockingham County since 1997. It is drained by the Piscassic, Little and Exeter rivers.

Long before Europeans settled the area, Brentwood was home to the Pennacook Abenaki tribes which farmed, fished and hunted there. Two main foot trails ran through the town, one along the Exeter River, where arrowheads and other stone and wooden artifacts have been found. At Pickpocket Dam, this pathway joined with the historic Pentucket Trail leading to Haverhill, Massachusetts, or points north.

The town was once a part of Exeter known as Brentwood Parish. It was named after Brentwood, Essex, originally called "Burnt Wood", where, in 1177, King Henry II granted permission for 40 acres (160,000 m²) of the king's forest to be cut, burned and cultivated. As early as 1738, residents living in the southwestern portion of Exeter, now Brentwood and Fremont, petitioned to be set off, but were denied. On 26 June 1742, however, permission was granted, and Brentwood was incorporated by Colonial Governor Benning Wentworth.

But almost from the beginning, a dispute arose between districts regarding the placement of a meetinghouse. It divided the community. Consequently, Gov. Wentworth, acting without approval of the General Assembly, in 1744 issued a King's Patent to establish a new town within Brentwood called Keeneborough Parish, named after his friend, Sir Benjamin Keene (1697–1757), English minister to Spain. Factions reconciled in 1750, when Keeneborough reunited with Brentwood.

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