The earlier part of the present mansion at Plas Coch was built by Dafydd Llwyd, an Anglesey lawyer living in London, in 1569. It was remodelled later in the last decade of the sixteenth century by his son Hugh Hughes, attorney general for North Wales from 1587, in a distinctive earlier Renaissance style with ornate crow-stepped gables. Substantial additions were made in the earlier nineteenth century and the house was again remodelled later in the same century producing a symmetrical facade in the style of the late sixteenth century house.

The sixteenth century house is a two storey building with cellars and attics. The walls are of coursed stone blocks under a slate gabled roof. It faced east where the facade was broken up by a full height porch and a smaller projecting bay, both with stepped gables. The windows are mullioned and transomed under pointed pediments, that over the porch doorway projecting as an oriel. The attics are lit by crow-stepped gables, topped with finials, as are all the gables. The porch presumably opened into the passage at the lower end of the hall, which has a fireplace in its long west wall. There is a large room beyond the hall, now the library. Service rooms and/or a parlour would have taken up the bay below the passage and would have communicated with the kitchen in a large rear wing. The tower in the angle between the hall and kitchen wing rises to overtop the house with an ogee roof.

The nineteenth century work was undertaken by an un-named Chester architect for William Bulkeley Hughes M.P.. The Elizabethan north walls were taken down and their red stonework reused for the third tower and other features on the front. Every window light was fitted with a small-paned Gothick casement; the stair-tower dome was replaced with a striking square-plan bell roof.

The house was re-developed in 2008-9 by Donald Insall Associates.

The house stands within extensive grounds and gardens, enclosed in a park (NPRN 265409). There is a seventeenth century barn to the south of the house (NPRN 31086).

Sources: RCAHM Anglesey Inventory (1937), 55-6
CADW Listed Buildings Database (19736)
Haslam, Orbach and Voelcker (2009), The Buildings of Wales: Gwynedd. Pevsner Architectural Guide, page 157.

RCAHMW, 2008

Tree-ring dating commissioned by North-West Wales tree-ring dating project in partnership with RCAHMW in 2010/11.
A total of 14 timbers were sampled from the roof of this building, including 2 from the principal rafters of a cusped truss thought to be of earlier origin. One of these two principal rafters was found to be from a tree felled in summer 1534. The remaining roof timbers probably represent a single group of trees felled at about the same time, though the narrow-ringed sequences were found to contain more sapwood rings than usually encountered in Wales. A single series was from a tree felled in spring 1592, with others having estimated felling date ranges either incorporating this date, or slightly earlier. Since it appears the rest of the roof, other than the cusped truss, is likely to have been constructed in a single campaign, this is most likely to have taken place in 1592, or within a few years after this date.
Full report available in NMRW. (NJR, 07/04/2011)

Additional: Tree-ring dating with site description reported in Vernacular Architecture 42 (2011). (RFS/RCAHMW/July 2011)