 Although the school's postal address is in Dorset, its site lies just over the county border in Wiltshire, within the parish of Donhead St Mary.St Mary's was founded in 1945 by the nuns of the Institute of the Blessed Virgin Mary (also known as the Sisters of Loreto) whose principles are based on the life and works of The Ven Mary Ward.Hence it has the same motto as its sister schools in Ascot and Cambridge.