Fish trap and mill races, Mary Brook Mills, 11 Raleagh Road, Drummaconagher, Crossgar, Downpatrick, Co. Down, BT30 9JG

Mary Brook Mills is an extensive and largely complete small-scale rural milling complex of Georgian vernacular character, dating from the 18th and early 19th centuries. Located at the end of a lane to the west of Raleagh Road, roughly 2½ miles east of Ballynahinch, the complex sits picturesquely beside the Ballynahinch River with a mill pond to the south.

The main buildings comprise two water-powered mills of mid to late 18th-century date: a two-storey corn mill and a two-storey flax mill, together with a single-storey stable block of the same period. These are complemented by a two-storey miller's house built in 1837 and subsidiary structures including a large two-storey barn (originally used as a barn, built around 1837), a cottage, and a storehouse of circa 1840s date. A smaller projection to the north of the corn mill and a two-storey barn to the south of the house were also added around 1837, with the storehouse to the north of the flax mill being shown on the revised Ordnance Survey map of 1858.

All buildings share a uniform appearance with harled and whitewashed facades, slated roofs, and Georgian paned sash windows with timber sheeted doors. The setting is enhanced by traditional wrought iron farm gates, stone walling, and simple gate pillars.

The site's water systems are integral to its character. Two mill races, lined in rubble stone for part of their length and in good condition, thread through the complex. A fish trap—a small, low L-shaped structure with timber walls, a slated gabled roof, and shaped barges—stands over the mill race to the south of the flax mill. The mill pond lies to the south and southeast.

Ordnance Survey maps of 1834 and 1836 valuation records confirm that the corn mill, flax mill, and stable were already established by this date. The original miller's residence, believed to date from the early to mid 18th century, was replaced by the present two-storey house in 1837, possibly incorporating some of the older fabric. The 1861 valuation records the complex under Christiana Silcock, lessee of Alexander John and Robert Stewart Esq., and lists numerous agricultural and milling buildings.

At its height in the late 19th century, Mary Brook employed around 150 workers in corn and flax milling, and in a small hemstitching factory situated in a building along the main drive off Raleagh Road. The hemstitching factory closed around 1900, the flax mill ceased production a few years later, and the corn mill continued in full-time use until after the First World War, with production halting by the 1930s. The complex was abandoned in the 1950s and fell into decay.

In the early 1970s it was acquired by Lewis-Crosby, a senior figure within the National Trust, who restored the buildings and brought the corn mill back into working order. The present owner acquired the complex in 1998. The corn mill operated until the late 1990s but was not in use at the time of the survey in October 2000.

The fish trap, mill pond, and mill races form an important part of the site's setting and archaeological interest, though they are not considered appropriate for listing protection.