[citation needed] During the late 17th century, the estate was owned by Nicholas Barbon, a developer who mortgaged it to Child's Bank and then died in debt around 1698.

Adam's design, which incorporates some of the earlier structure, is highly unusual, and it differs greatly in style from the original construction.

One side is left almost open and is spanned by an Ionic pedimented screen, which is approached by a broad flight of steps and leads to a central courtyard, which is at piano nobile level.

[7] The rooms are characterised by elaborate but restrained plasterwork, rich, highly varied colour schemes, and a degree of coordination between decor and furnishings unusual in English neoclassical interiors.

When Child died two months later, his will placed his vast holdings, including Osterley, in trust for any second-to-be born grandchild.

George Child Villiers, 9th Earl of Jersey, opened Osterley to the public in 1939 after having received many requests from people wishing to see its historic interior.

[9] Villiers staged a series of exhibitions of artworks by living artists in the top-floor rooms to contrast with the 18th-century interiors on the ground floor.

[9] The grounds of Osterley Park were used for the training of the first members of the Local Defence Volunteers (forerunners of the Home Guard) when the 9th Earl, a friend of publisher Edward George Warris Hulton, allowed writer and military journalist Captain Tom Wintringham to establish the first Home Guard training school (which Hulton sponsored) at the park in May–June 1940.

[10] Painter Roland Penrose taught camouflaging here, an extension of work he had developed with the paintbrush in avant-garde paintings to protect the modesty of his lover, Elizabeth 'Lee' Miller (married to Aziz E.

[10] After the Second World War, Lord Jersey approached Middlesex County Council, which had shown interest in buying the estate, but eventually decided to give the house and its park to the National Trust.

The house has enjoyed loans and gifts from Lord Jersey, including items of silver, porcelain, furniture and miniatures.