Cornelis de Graeff (15 October 1599 – 4 May 1664), often named Polsbroek or de heer van (lord) Polsbroek during his lifetime, was an influential regent and Burgemeester (Borough Master or Mayor) of Amsterdam, statesman and diplomat of Holland and the Republic of the United Netherlands at the height of the Dutch Golden Age. He was the most illustrious member of the De Graeff family, which in the Golden Age originally held political power together with the Bicker family and by marriage in Amsterdam Holland and finally the Dutch Republic.

De Graeff belonged to the republican political movement also referred to as the state oriented, the Dutch States Party, as opposed to the Orangisten and opponent of the political ambitions of the House of Orange. He was one of the leading figures who sought to end the Eighty Years' War between the United Netherlands and the Kingdom of Spain, which took place in 1648 with the Peace of Münster. Inside Amsterdam De Graeff became the moderate successor to his ultra-republican cousin Andries Bicker. In the following era after the sudden death of stadholder William II of Orange, the First Stadtholderless Period, which was promoted by De Graeff, he and his nephew Grand pensionary Johan de Witt were regarded as the leading republican protagonists.

The progressive cooperation between De Graeff and his protégé, De Witt, was an important political axis that ordered the political system within the republic. Both belonged now to the two republican and state-minded families where political power within Holland rested primarily with. In Amsterdam this lay with the brothers Cornelis and Andries de Graeff, and in The Hague with the brothers Cornelis and Johan de Witt. Until his death in 1664, De Graeff was Amsterdam's leading politician, then the republican center of the republic. However, he not only had the interests of these in mind, but also those of Holland and the political settlement with the other provinces.

De Graeff was considered a prudent and skilful statesman and diplomat who was concerned about the balance between the religious and political factions and was held in high esteem by the population. His political stance was characteristic of his family: on the one hand libertine and state-minded, on the other hand, if only to a limited extent, loyal to the House of Orange. The proponents of the De Graeff family has shown they had an eye for national politics and tried to find some balance between the House of Orange and the Republicans. They were against too much influence of the church on political issues. After his death, his younger brother Andries de Graeff continued the De Graeff faction and its republican and more liberal politics. Like his brother, Andries De Graeff, he was an art collector and patron of the arts. De Graeff was Free Lord of Zuidpolsbroek, Ambachtsheer (Lord of the manor) of Sloten, Sloterdijk, Nieuwer-Amstel, Osdorp and Amstelveen and acted as President of the Dutch East Indies Company.

Cornelis de Graeff was the oldest son of Jacob Dircksz de Graeff, burgomaster of Amsterdam and Vrijheer of Zuid-Polsbroek, and his wife Aeltje Boelens Loen, member of the family Boelens Loen, one of the oldest patrician families of Amsterdam and great-great-granddaughter of the important late medieval Amsterdam city regent and burgomaster Andries Boelens. His father was of free-thinking, republican sentiment, but also known for his obsession with fame. He was one of the leading Remonstrants and state-loving patricians, who was nevertheless not a principled anti-Orangist (supporters if the House of Orange-Nassau). He honored the inheritance of his father, Dirck Jansz Graeff, who was on friendly terms with William the Silent of Orange. The young De Graeffs were influenced by their father's antagonistic attitude towards political issues.

The relationship between the leading patriciat was very close. Four of Cornelis ' siblings married members of the Bicker family. One of his sisters Agneta de Graeff van Polsbroek married Jan Bicker. The couple had Wendela Bicker and Jacoba Bicker among others; Wendela married to Grand pensionary Johan de Witt and Jacoba to his own son Pieter de Graeff. His close relatives included also Hollands writer and poet Pieter Corneliszoon Hooft as one of his uncles, the influential Amsterdam burgomasters and statesmen Andries, Cornelis, Jan Bicker who were his cousins, and burgomaster Frans Banning Cocq (captain of Rembrandt's painting The Night Watch), who was his brother-in-law. He was also linked to the noble family of Van Hogendorp by marriage and burgomaster Joan Huydecoper van Maarsseveen was his great cousin.

Cornelis de Graeff said that the ancient Amsterdammers had no habit of keeping genealogical records of their families, and knew no more of their generation than what they have learned from their fathers and grandfathers. The dates of his own family in Amsterdam do not go back very far:

And first I'll start with the family de Graven from which I descended on my father's side. This is a family from Amsterdam, coming from the house 'de Keijser', that was located at the Waeter (= now Damrak No. 91). This house shows the impression of its vaulted appearance, owned by Jan Pieters de Graeff, and then by Dirck Jans de Graeff, who also sold this house. My father Jacob de Graeff and his brothers were also born here.