Blessington House, 18 Ballynahinch Street, Hillsborough, County Down, BT26 6AW

Blessington House is a mid-terrace, four-bay, two-storey late 18th-century rendered townhouse with an entrance portico and a front railed area, built around 1780 as a residence of suitable grandeur for the Marquis of Downshire's agent. Together with its neighbouring properties at Nos. 16A/16B and 20 Ballynahinch Street, it was originally conceived as a single large house, and its design was based on a similar building — the Downshire Hotel — in Blessington, County Wicklow, part of a separate estate inherited by the first Marquis of Downshire in 1778. The house exhibits fine Georgian proportions and makes a significant contribution to the architectural and historic heritage of Hillsborough.

The building is rectangular on plan, facing south, with a two-storey return to the west and a canted stairhall projection to the east. The pitched roof is covered in natural slate with black clay ridge tiles, and there is a pair of off-centre rendered chimneystacks. Cast-iron guttering sits on shaped iron brackets to an ogee-moulded sandstone eaves course, with cast-iron hopper and downpipe. The external walls are finished in ruled and lined lime render over rubble, with rusticated sandstone quoins and a projecting sandstone plinth course. Window openings are square-headed with moulded architrave surrounds, sandstone sills, and original timber sash windows throughout.

The south-facing front elevation is five windows wide, with the southernmost bay incorporated within the lower ridge of the adjoining No. 16. The easternmost bay features a prostyle Ionic sandstone portico — one of the principal focal points of the street — comprising two pairs of Ionic columns supporting an architrave and full entablature, with corresponding Doric pilasters set at the plane of the façade. The first-floor windows are 6/3 timber sashes and the ground-floor windows are 6/6 timber sashes, some retaining cylinder glass.

The doorway within the portico is a three-centred arched opening with a moulded archivolt. The original timber door has four raised and fielded panels and brass furniture, and is flanked by sidelights and slender pilasters bearing Greek key motifs on sandstone bases, which support a moulded lintel cornice. Above is a glazed fanlight with margin lights. The door opens into a sandstone-flagged portico containing a pair of wrought-iron bootscrapers. In front of the house, a small concrete-paved area is enclosed by decorative cast-iron railings on a low stone plinth wall, with an incorporated wrought-iron lamp standard.

The west side elevation is abutted by the adjoining No. 16. The rear elevation is abutted by the two-storey canted stairhall projection to the east and the two-storey gable-ended return to the west. The stairhall features a double-height round-headed 8/12 timber sash window. The remainder of the rear elevation is largely glazed with 6/6 timber sash windows, including one early example with an exposed sash box. To the centre of the rear elevation is a square-headed door opening with a raised and fielded panelled door and sidelights. In the re-entrant angle of the return there is a diminutive projection with a natural slate roof. A further square-headed door opening in the return retains its original sheeted timber door. The rear entrance opens onto a rear yard with some original cobbles. The east side elevation is abutted by the adjoining No. 20.

The listing extends to the house, railings, and lamp as an ensemble.

In terms of setting, Blessington House forms part of a terrace of three similar houses lining the north side of Ballynahinch Street. Access to the rear is through a carriage arch in a screen wall abutting the east gable of No. 20, which leads into a cobbled rear yard enclosed by a two-storey rendered former outbuilding — now converted to residential use — whose rear elevation forms the boundary of the yard. The former servants' quarters have similarly been converted into a separate dwelling.

The history of the house is well documented. It first appears on a map of Hillsborough dating from around 1800, where it is depicted as a large oblong building incorporating what is now No. 20. The 1833 Ordnance Survey map shows the house with a large L-shaped rear return and a number of outbuildings. The Townland Valuation of the 1830s records a Mr. William Edmond Reilly as occupant, with the house valued at £34. Reilly was the last MP to sit for the Hillsborough Constituency before the dissolution of the Irish Parliament under the Act of Union in 1801. By 1843 he held the posts of Deputy-Lieutenant for County Down and Justice of the Peace, and his gravestone describes him as the "confidential friend and agent to the third Marquis of Downshire for the long period of 41 years, during which time he gained the real esteem and respect of all by his kindness, urbanity and unflinching integrity."

In 1861, Nos. 18–20 were still recorded as a single dwelling, by then valued at £54 and occupied by a Mr. Fitzherbert Filgate, also a Justice of the Peace for Hillsborough and a Trustee for the North East Agricultural Association of Ireland. Griffith's Valuation records the combined property as measuring 25 yards by 5 yards, with a large number of outbuildings in the rear courtyard. The second edition of the Ordnance Survey (1858) shows little change to this layout. It was not until 1871 that the house was divided into two separate dwellings under a new occupant, Major Henry Stanley McClintock (1812–1898), who had served with the Royal Horse Artillery and the Antrim Artillery and later became a Justice of the Peace for County Down. Following the division, No. 18 was used as premises for the Hillsborough Woollen Company, valued at £26, while No. 20 was taken over by the Northern Bank Company. It is also noted that the Marquis of Downshire at one point considered demolishing Blessington House in order to alter the course of the street, and that after 1870 the official residence of the agent was moved to Kilwarlin House on Lisburn Street. One authority suggests that Nos. 18 and 20 were always intended as separate dwellings — Blessington House being used by the agent and the other by his sub-agent — despite being valued as one until 1871.

No. 18 was briefly occupied by the Rev. J. Moorhead in 1888 and Samuel R. Robinson in 1893. A Ms. Charlotte Payne occupied the house from 1897 until her death in 1911. The 1901 census records Payne, aged 70, living at No. 18 with her two daughters and her son Henry William Payne, who worked in the adjoining Northern Bank. The building return at that time classifies the house as a first-class dwelling of 13 inhabited rooms, with no outbuildings recorded. By 1911, Henry Payne had become the occupant following his mother's death, and he remained there until 1920, when a Mr. Charles A. Horsburgh took possession and lived there until the end of the Annual Revisions in 1930. The manager of the adjoining Northern Bank was still occupying Blessington House as late as the 1970s.

The house was listed in 1976. Between 1978 and 1990 a number of renovations were carried out, and in 2005 the front elevation was fully restored.