Plas Machynlleth is the former Welsh residence of the Marquesses of Londonderry. It is situated in the market town of Machynlleth in Powys (formerly Montgomeryshire), Wales. It was brought into the family following the 1846 marriage of the then Viscount Seaham (who later became, in March 1854, Earl Vane, and in November 1872 the 5th Marquess of Londonderry) to Mary Cornelia Edwards, who inherited it on the death of her father, Sir John Edwards, in 1850. Sir John had extended and renamed the house. It is a Grade II* listed building[1] and its gardens, now mainly a public park, are listed on the Cadw/ICOMOS Register of Parks and Gardens of Special Historic Interest in Wales.