Margaret Cavendish Harley was born 11 February 1715 in Welbeck Abbey, Nottinghamshire, England, United Kingdom to Edward Harley, 2nd Earl of Oxford and Earl Mortimer (1689-1741) and Henrietta Cavendish Holles (1694-1755) and died 17 July 1785 Bulstrode, Buckinghamshire, England, United Kingdom of unspecified causes. She married William Bentinck, 2nd Duke of Portland (1709-1762) 11 July 1734 Oxford Chapel in Marylebone, Middlesex, England, United Kingdom.
|Offspring of William Bentinck, 2nd Duke of Portland and Margaret Cavendish Harley (1715-1785)|
|Elizabeth Cavendish-Bentinck (1735-1825)||27 July 1735||12 December 1825 Lower Grosvenor Street, London, Greater London, England, United Kingdom||Thomas Thynne, 1st Marquess of Bath (1734-1796)|
|Henrietta Cavendish-Bentinck (1737-1827)||8 February 1737||4 June 1827||George Harry Grey, 5th Earl of Stamford (1737-1819)|
|William Henry Bentinck, 3rd Duke of Portland (1738-1809)||14 April 1738 Welbeck Abbey, Nottinghamshire, England, United Kingdom||30 October 1809 Bulstrode Park, Buckinghamshire, England, United Kingdom||Dorothy Cavendish (1750-1794)|
|Margaret Bentinck (1739-1756)|
|Frances Bentinck (1741-1743)|
|Edward Charles Bentinck (1744-1819)|