His uncle was Johan de Witt, Statesman of the True Freedom, husband of Wendela Bicker, sister of Cornelis' mother Jacoba.

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.

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.

[3] The personal coat of arms of Cornelis de Graeff is quarterd with a heart shield and shows the following symbols: