His parents were
Pieter de Graeff and his cousin
Jacoba Bicker, his younger brother was
Johan de Graeff, the
Free Lord of Zuid-Polsbroek. His uncle was
Johan de Witt, Statesman of the
True Freedom, husband of
Wendela Bicker, sister of Cornelis' mother Jacoba. Cornelis de Graeff was a
Canon of
St. Pieter at
Utrecht. Most of the time he resided at his castle
Ilpenstein. He also owned
Bronstee, a country estate near
Heemstede. De Graeff was mentally disturbed and remained unmarried. Since his father's death in 1707 he was under the tutelage of Jacobus de Fremeri, and died at his castle Ilpenstein on February 16, 1719. His successor as
Free Lord of Purmerland and Ilpendam was his cousin
Gerrit de Graeff. Cornelis' burial chapel is in the Oude Kerk in Amsterdam, in the Sint Cornelis choir, the family grave of the De Graeff family. At Ilpenstein castle De Graeff had a famous art collection, including
Rembrandts
Jacob Blessing the Sons of Joseph (the sitters were
Wendela de Graeff and her two sons) and the
Portrait of Andries de Graeff. The two famous paintings, both by Rembrandt, can be seen today at
Wilhelmshöhe in
Kassel. De Graeff also owned
Frans Halsens painting
Catharina Hooft with her Nurse. In 1710 a copy of Rembrandt's 'The Night Watch' was assigned to him. Around 1712, De Graeff's curator De Fremery sold the piece to
Pieter van der Lip. Rembrandt expert
Abraham Bredius suspected that a second copy of 'The Night Watch', painted by
Gerrit Lundens, had gone to Cornelis de Graeff; which turned out to be correct. A painting after Lundens was also present at Pieter de Graeff, after the well-known drawing in the album by De Graeffs uncle
Frans Banninck Cocq. This album has been owned by the De Graeff family since 1678. ==Coat of arms==