Mary Dendy (28 January 1855 - 9 May 1933) was a promoter of residential schools for mentally handicapped people, i.e. institutionalisation. Dendy was the driving force that established a colony for the "feeble-minded". Dendy believed in separate development to avoid crime and these people passing their problems on to their children. She joined the Eugenics Education Society.
Dendy was born in 1855 in Bryncelyn in North Wales. She was the daughter of John Dendy, Unitarian minister, and his wife Sarah Beard (1831–1922), eldest daughter of John Relly Beard. Her sister was the social reformer Helen Bosanquet and her brother was the biologist Arthur Dendy (1865–1925).
Dendy became interested in the care of the "feeble-minded" in Manchester where she sat on the School Board from 1898. She believed that these children needed to be housed in institutions after conducting a survey of Manchester school children. She, aided by Dr Henry Ashby, persuaded the board to open special schools for the "feeble-minded". She believed that these children were the result of alcohol and poverty and without the intervention of society then these weaknesses would be inherited by future generations. In 1908 the Sandlebridge Boarding School or Sandlebridge Colony was opened by Incorporated Lancashire and Cheshire Society for the Permanent Care of the Feeble Minded. This charity had been started by members of the Manchester School Board starting in 1898. The schools were opened to residents who had been at Sandlebridge since 1902. This society ran the homes until the local authority took over en route to becoming part of the National Health Service in 1945. In 1933 the society had changed the name to the Mary Dendy Homes, and these came to be known as the Mary Dendy Hospital.
Dendy was the driving force that established a colony for the "feeble-minded". Dendy believed in separate development to avoid crime and these people passing their problems on to their children. She joined the Eugenics Education Society some time after 1900.