The Upper Hutt Blockhouse was built in Trentham, Upper Hutt in 1860 and is one of a number of defences built in the Wellington area in response to a perceived threat of Māori attack on Pākehā settlers. Its construction illustrates the deterioration in relations between Māori and Pākehā in the 1860s and it is a very rare surviving example of this type of defensive building in New Zealand. The place is also historically significant as the legal protection given in 1916 is one of the first recorded examples of statutory protection of a historic building in New Zealand.

Fighting in the Taranaki area in 1860 caused Hutt settlers to fear attack by local Māori. There were alleged disturbances in and around the Wellington and Wairarapa districts and rumours that Wairarapa Māori were planning to advance over the Rimutakas. Alarmed settlers held a series of meetings in the Hutt Valley, and it was decided to build two blockhouses as a precautionary measure – one in Upper Hutt and one in Lower Hutt.

The two-storeyed blockhouse was designed by Colonel Thomas Rawlings Mould of the Royal Engineers and erected in the centre of the existing Upper Hutt settlement. The L-shaped building was at the north corner of a nine foot [three metre] high stockade atop a large defensive earthwork. Constructed of local tōtara, the blockhouse was weatherboarded on the exterior and the interior lined with inch-thick boards. The cavity was filled with fine gravel to absorb the impact of gunfire. The exterior walls on both floors had a series of balistraria, or loop holes, through which guns could be fired. The holes were filled with tampions - shaped solid timber elements designed to fit into the loopholes. The ground floor had two large rooms, the larger of which contained the staircase and a small store room. The upper floor was one large space with long balistraria (narrow openings) facing inwards. The roof was of tōtara shingles.

A small militia initially occupied the blockhouse; however, as the feared attack never eventuated, they left in May 1861. From 1867, the place was used as a police house, courthouse and residence. In 1884, the building was occupied by the Lands and Survey Department. Five years later, control of the land was given to the Upper Hutt Council. In 1916, following representations from local people interested in the preservation of the blockhouse, the land was reserved under the Scenery Preservation Act 1908. The building was substantially repaired in 1927-1928 and windows added on the inner side of the L-shaped structure. By this stage the control of the blockhouse itself was vested in the Upper Hutt Council. From 1953 until the late 1990s, local boy scouts and girl guides used the building. It has also been used for meetings of the Upper Hutt Round Table.

In 1980, the place was classified as a historic reserve under the Reserves Act 1977 and the New Zealand Historic Places Trust (now Heritage New Zealand) was appointed as manager. The earthworks have been flattened to form part of the school playing fields that now surround the blockhouse, however they are visible at times due to differential grass growth. In 2014, as well as some repiling and drainage improvements, the building was seismically strengthened, which required most of the river gravel to be removed from the wall cavities. The remaining gravel can now be viewed via a small panel in the wall.