The two-storeyed Blockhouse was erected in the centre of the existing Upper Hutt settlement, and had associated earthworks and a stockade. Although the earthworks and stockade are no longer visible, the building’s features such as local tōtara weatherboards, gravel-filled walls, and balistraria, or loop holes, through which guns could be fired, are still present.

The Blockhouse was occupied by a small militia from late 1860 until May 1861, but saw no action. From 1867, the building was used as the local police house, courthouse and residence.