Northern Bank, 20 Ballynahinch Street, Hillsborough, County Down, BT26 6AW

This is a late 18th century former house, built around 1780, now in use as a bank. It sits at the end of a terrace on the north side of Ballynahinch Street, Hillsborough, facing south, and was originally constructed as a residence for the Marquis of Downshire's agent. The listing covers the bank building itself, its railings, and the yard wall.

The building is two storeys, rectangular on plan, with a pair of later rear returns. It was originally part of a single large house together with the neighbouring properties at Nos. 16A/16B and 18 Ballynahinch Street, before being subdivided. The roof is pitched natural slate with black clay ridge tiles and two rendered chimneystacks. The east gable has a concrete coping, and a sandstone eaves cornice runs along the front, fitted with shaped iron brackets supporting cast-iron guttering and downpipe.

The walling is ruled and lined lime render, with painted masonry rusticated quoins and a smooth render plinth course. The front elevation is five windows wide and symmetrically composed. Window openings are square-headed with architrave surrounds and original timber sash windows throughout: six-over-three panes to the first floor, six-over-six to the ground floor (the top-right window is blind), and painted masonry sills. To the rear, windows are generally six-over-six timber sashes, with a tripartite timber sash window on the exposed rear elevation. The east gable carries a pair of six-over-three sashes to the first floor and six-over-six sashes to the ground floor.

The front door is square-headed, with a replacement timber door having four raised and fielded panels and a rectangular overlight above. The doorcase is a handsome stucco composition flanked by a pair of engaged Ionic piers with entasis, supporting a plain architrave and entablature covered in lead. The door opens onto a stone threshold and a gentle concrete ramp, enclosed on either side by decorative cast-iron railings set on a low painted stone plinth wall. The enclosed areas to either side are tiled. To the west section, a decorative iron lamp standard is present, though the railing here has been broken to provide access to an ATM machine installed in 1990. The west side elevation is abutted by the adjoining No. 18.

To the rear, two two-storey returns adjoin the main building: the eastern return has a pitched slate roof and the western a flat roof. The lower east return runs flush with the east gable, abutted by a tall round pier, and has pebbledash rendered walling with a single timber casement window. A tall lime-rendered screen wall abuts the east end of the front elevation, with painted masonry coping and a large round-headed arch, which gives access to a number of dwellings to the rear.

Internally, the first floor retains its original character to a greater degree than the ground floor. Surviving features on the upper floor include a staircase, some original cornice work, and doors. Very few original features remain on the lower floor.

The setting comprises a small rear paved yard enclosed by a tall rubblestone wall, with a lean-to red brick shed having steel windows. Together with Nos. 16A/16B and 18 Ballynahinch Street, the building forms part of a terrace of three similar houses that once constituted a single dwelling lining the north side of the street.

Historically, the building first appears on an early map of Hillsborough dating to around 1800, at which point it formed a single oblong structure with No. 18. The 1833 Ordnance Survey showed the combined property possessed a large L-shaped rear return and several outbuildings. In the 1830s the Townland Valuation recorded the occupant as Mr. William Edmond Reilly, with the house valued at £34. Reilly was the last Member of Parliament to sit for the Hillsborough constituency in the Irish Parliament before its dissolution under the Act of Union in 1801. By 1843 he held the posts of Deputy-Lieutenant for County Down and Justice of the Peace. 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."

By 1861 Nos. 18–20 were still recorded as a single dwelling, valued at £54 and occupied by Mr. Fitzherbert Filgate, a Justice of the Peace and Trustee of the North East Agricultural Association of Ireland. Griffith's Valuation records the combined property as measuring 25 yards by 5 yards with numerous outbuildings in the rear courtyard. The second edition of the Ordnance Survey (1858) showed little change to the layout.

It was not until 1871, under a new occupant, Major Henry Stanley McClintock (1812–1898), that the house was divided into two separate dwellings. McClintock had served with the Royal Horse Artillery and the Antrim Artillery, and later became a Justice of the Peace for County Down. At that point No. 18 was taken over by the Hillsborough Woollen Company, and No. 20 was converted into a branch of the Northern Bank, revalued at £23. The Annual Revisions map of around 1865 depicts the Northern Bank as a square building with a small rear return.

Scholarly sources offer slightly differing accounts of the building's earlier history. Barry states that Nos. 18–20 were built around 1780 as a home for the Marquis of Downshire's agent, who lived there until 1870 when the agent's official residence was moved to Kilwarlin House on Lisburn Street. Walker notes that the Marquis of Downshire considered demolishing Blessington House and No. 20 Ballynahinch Street in order to alter the course of the street. Brett, however, suggests that Nos. 18 and 20 were always intended as separate dwellings — one for the agent and one for his sub-agent — despite being valued as a single residence until 1871. Until the 1970s the Bank Manager's residence was in Blessington House.

The building was listed in 1976. In 1990 a section of the original railings was removed to accommodate the ATM installation. In 2004 the windows were restored, and further restoration work was completed by the time of the site assessment in 2010.