Plas Machynlleth was the Welsh residence of the Marquesses of Londonderry. It was bought into the family by the marriage of George Henry Robert Charles William Vane-Tempest, 5th Marquess of Londonderry to Mary Cornelia Edwards.
The house is in the village of Machynlleth, on the coast of Wales and was the home of the Londonderry family for generations. The building of the house stretches over 200 years, with the oldest parts dating back to the 1600s while the main entrance front was added in 1853. The house was called Greenfields for many years. It was later named after the village nearby.
Charles Stewart Henry Vane-Tempest-Stewart, 7th Marquess of Londonderry dedcided to give the mansion and its estate to the village and the house was used for council offices. Now it is the home of the 'Celtica' heritage centre.