Trevor House, 9 The Square, Hillsborough, Co. Down, BT26 6AG

Trevor House is a semi-detached three-storey over basement rendered Georgian townhouse, built around 1740, forming one of a pair with its neighbour No. 8 The Square. It faces north on the south side of The Square, on the corner of Dromore Road, and is one of the oldest surviving buildings in this part of Hillsborough.

The house is rectangular in plan with a railed basement area. The roof is pitched natural slate with black clay ridge tiles, and a large rendered chimneystack rises from the west gable. Cast-iron guttering, supported on iron brackets, is fixed to a moulded sandstone eaves cornice that returns to the gable, with a cast-iron downpipe below. The external walls are dry-dash rendered with smooth render quoins and a painted render plinth course above the basement.

All window openings are square-headed with smooth render surrounds, painted masonry sills, and timber sash windows. The front north elevation is four windows wide, with the door opening positioned in the left bay. Much of the original glazing survives: the second floor has 3/3 sash windows, the first floor has 6/6 sash windows, all without horns and retaining cylinder glass. The ground floor has replacement 6/6 timber sash windows with ogee horns on a continuous sill course, and the basement also has later 6/6 replacements.

The entrance is a round-arched door opening with a painted quadrant moulded surround featuring impost mouldings and a keystone. The original timber door has six raised and fielded panels above three flush panels, with a lintel cornice and a webbed timber fanlight over. The threshold is a replacement granite step, opening onto a granite paved platform shared with the neighbouring No. 8. Five granite steps, enclosed by original wrought-iron railing on a low rendered plinth wall with stone coping, descend to the basement area.

The west gable is blank, facing onto Dromore Road. The rear elevation is four storeys and three windows wide at basement and ground floor level, reducing to two windows wide at first and second floor level. The irregular window pattern reflects windows serving the half-landings, and there is a round-arched window opening at ground floor level with a sandstone surround that is partly blocked up. The rear windows are largely original, with 3/3 sashes to the second floor and 6/6 sashes to the remaining floors. A lean-to extension at basement level, built around 1980, spans almost the entire rear elevation. The east elevation is abutted by the neighbouring No. 8.

The house is set on a slender plot between Dromore Road to the west and Park Lane to the east. Together with its neighbour, it dominates the south side of The Square, overlooking the former Market House and Hillsborough Castle, and also dominates the long streetscape of Main Street when viewed from the north end. To the rear is a small stone-paved garden enclosed by rubblestone walls, accessed via a brick-lined pedestrian entrance to Dromore Road.

Historically, Trevor House originated as part of a terrace conceived under the plans of Lord Hillsborough — Wills Hill, later first Marquess of Downshire — to develop the town and encourage linen manufacturing. The terrace is visible on a map of 1745 and is specifically referenced in Walter Harris's survey of County Down published in 1744, which records that Lord Hillsborough "has already erected two Ranges of commodious Houses, to each of which are annexed a Garden" as part of his plan for a new town built around a large square with a market house at its centre. The remainder of the original terrace was partially demolished by 1833 as part of a subsequent Lord Downshire's scheme to re-route the Moira Road away from Hillsborough Castle, and had been completely cleared by 1858. An estate map of around 1800 records the occupant of this house as a Mr Hanna, showing the building as rectangular in plan with outbuildings to the rear.

The name 'Trevor House' was among those given to houses on the Square by Lord Arthur Hill, younger brother of the fifth Marquess of Downshire, who lived at Hillsborough Castle during the last quarter of the 19th century. 'Trevor' most probably refers to Trevor Hill, Viscount Hillsborough, an 18th century ancestor of the Downshire family.

In the Townland Valuation of 1828 to 1840, this house and its neighbour are recorded as a single dwelling occupied by Henry Jefferson and valued at £16 16 shillings. By the time of Griffith's Valuation of 1856 to 1864, the building had been divided into two separate dwellings. The current house was at that point occupied by Sarah Lutton, who leased it from the Marquess of Downshire. It was recorded as a house and yard valued at £14, with a rent of £10 noted as 'low'. The record specifies dimensions for a private house, a basement, and an office. At this period, many other properties on the Square were in use as shops or public houses, making this house's continued residential use notable.

The house remained in the Lutton family for some years before being taken over in 1876 by the Freemasons for use as a Masonic Hall and yard. By 1891 it had returned to private residential use, with a succession of tenants: John Alexander Knox in 1891, Thomas S. Howe in 1896, Elizabeth Wilcox in 1902, James Armstrong in 1907, and Charles D. Macown in 1909. The building was listed in 1976 and has since been used as offices by various professional practices for over twenty years. A private flat at basement level is accessed from the rear yard.