 This made her chatelaine of several large houses designed for entertaining, notably Londonderry House, the family's London townhouse in Mayfair, and Mount Stewart, the family seat in County Down.They also owned other properties such as Seaham Hall and Wynward Park in County Durham, and Plas Machynlleth in Wales.During the 1920s, Lady Londonderry created the gardens at the Londonderry family estate of Mount Stewart, near Newtownards, County Down.