Plas Newydd, located in Llanfairpwllgwyngyll, Anglesey, Wales, is the country seat of the Marquess of Anglesey. The family's former principal seat at Beaudesert, Staffordshire, was sold and demolished in the 1930s.
The house is situated on the bank of the Menai Strait and has views of Snowdonia.
The estate can be traced to the 15th century when it was held by the Griffiths family, owners of a large estate in nearby Bangor. The house originated in the 14th century; the earliest section is the Great Hall with symmetrical entrances at either end. From there the house was expanded towards the Menai Strait and two towers were added.
The building was greatly altered in the 18th century by James Wyatt who refaced it, blended the towers into the building front, and substantially made it into the building that stands today. At the end of the 19th century the 5th Marquess had the chapel turned into a theatre. Plays were put on regularly, with the Marquess often taking the lead role himself. After the 6th Marquess inherited the estate, all the furniture was sold to help restore the solvency of the family after the 5th Marquess' huge spending. The family also sold off their main home and their London house and moved into Plas Newydd permanently. The 6th Marquess made the final big changes to the house by removing the crenellations from the roof, disposing of the theatre, knocking three servants' rooms together to make the dining room and covering over a courtyard to provide a roof for the servants.
The house has been owned by the National Trust since 1976. There are now a tearoom and a second-hand bookshop, and historical cruises along the Menai start from the house.
The house contains Rex Whistler’s largest painting, measuring 58 by 12 feet (18 by 3.7 m). It is the largest single canvas in Britain. There is also an exhibition with many examples of his work.
The 7th Marquess of Anglesey still retains rooms at the house. Lady Rose McLaren grew up at the house along with the 7th Marquess - her brother.
At the house there is also a Military Museum which contains campaign relics belonging to the 1st Marquess of Anglesey, mementos of the Battle of Waterloo and the Anglesey Leg.
In January 2010, the grounds became the first part of North Wales to be included in Google Street View, thanks to a scheme to include National Trust properties by using the Google Trike where vehicular access is limited.