Berllan-deg, Llanhennock, Monmouthshire is a country house dating from the mid-17th century. A rare survival of a remarkably unaltered hall house, Berllan-deg is a Grade II* listed building.

The architectural historian John Newman dates the building of Berllan-deg to "the second quarter of the 17th century". Cadw gives the dates of 1620–1640. Sir Joseph Bradney, in his A History of Monmouthshire from the Coming of the Normans into Wales down to the Present Time records the owner in 1635 as John ap Rosser Morgan, and notes that, by the early 18th century, the house was "let to tenant farmers". Sir Cyril Fox and Lord Raglan, in the third of their three-volume study Monmouthshire Houses, described Berllan-deg as "a fine hall-house". The house remains privately owned.

With the exception of a small extension on the garden front of the house, noted by Fox and Raglan during their visit in the 1950s, Berllan-deg is almost unaltered since its construction. Peter Smith records it as a cross-passage hall house, with a fireplace stair, and post-and-panel partitions. Fox and Raglan produce an illustration showing the house's three-room plan, divided by the cross-passage. Newman notes the "twisted timber stair" in the parlour, between a closet and the fireplace hearth. He considers that Berllan-deg represents the "native tradition (of vernacular architecture) at its fullest development" and the "substantial and little-altered house" has a Grade II* listing.

• Bradney, Joseph (1993). The Hundred of Usk, Volume 3 Part 2. A History of Monmouthshire. London: Merton Priory Press. ISBN 9780952000938. OCLC 30036988.
• Fox, Cyril; Raglan, Lord (1994). Renaissance Houses, c. 1590-1714. Monmouthshire Houses. Vol. 3. Cardiff: Merton Priory Press Ltd & The National Museum of Wales. ISBN 9780952000990. OCLC 877314571.
• Newman, John (2000). Gwent/Monmouthshire. The Buildings of Wales. London: Penguin. ISBN 0-14-071053-1.
• Smith, Peter (1975). Houses of the Welsh Countryside. London: Her Majesty's Stationery Office. ISBN 0-11-700475-8. OCLC 868639211.