Fonds GB 0210 PLAETH - Plas Machynlleth Estate Records (formerly Plas Machynlleth MSS and Documents and Londonderry Collection),

The first occupant of Plas Machynlleth (or Greenfields) was John Edwards (d. 1789), a Machynlleth solicitor, who purchased the property in the 1750s. He was the third son of Lewis Edwards of Talgarth, Merionethshire. His third wife was Cornelia Owen, daughter and heiress of Richard Owen of Garth, Llanidloes. This marriage bought to the family the Garth estate and the profitable Van lead mines. On the sale of parts of the Peniarth estate he acquired more property along the Dyfi Valley. On the death of his son, Sir John Edwards, in 1850, the estate passed to his daughter, Mary Cornelia.

In 1846 Mary married George Henry Robert Charles Vane-Tempest (d. 1884), second son of Charles William, 3rd Marquess of Londonderry. George succeeded his half brother, Frederick as the 5th Marquess of Londonderry in 1872. In 1873 the Marquess of Londonderry owned an estimated 10,084 acres in Wales (in Montgomeryshire and Merionethshire), with an estimated rental of £6,082. However, although owning estates in Ireland, County Durham and Londonderry House in London, the family made Plas Machynlleth their principal home.

After the death of George, 5th Marquess of Londonderry, Mary continued to reside at Plas Machynlleth until her own death in 1906. Her third son, Herbert Lionel Vane-Tempest, continued to live at Plas Machynlleth until his death in 1921. The estate then passed to Herbert's nephew, Charles Stewart Henry Vane-Tempest-Stewart, 7th Marquess of Londonderry, who did not reside at Plas Machynlleth. This, together with the burden of heavy taxation, forced the sale of most of the estate. In 1948 the 7th Marquess presented Plas Machynlleth and the parkland comprising some 40 acres to the town of Machynlleth. The estate was finally liquidated in 1951.