Willem de Kooning, son of Leendert de Kooning and Cornelia Nobel, was born on 24 April 1904 in Rotterdam.

Willem's parents separated when he was not yet two years old, and divorced a year and a half later. He lived with his father for three years, then went to live with his mother and stepfather. He moved to Brussels, Belgium, in or before 1925.

Leendert de Kooning, son of Willem de Kooning and Maria van Ladesteijn, was born on 10 February 1876 in Rotterdam.

He married Cornelia Nobel, daughter of Christiaan Gerardus Nobel and Cornelia Oers, on 29 December 1898 in Schiedam. She was born on 3 March 1867 in Schiedam.

Children of Leendert and Cornelia:

1. Maria Cornelia de Kooning, born on 2 July 1899 in Rotterdam. She married Dirk Breedveld, son of Antonie Breedveld and Neeltje de Groot, on 26 April 1916 in Rotterdam.

   She was raised by her mother and stepfather, but shortly after her 16th birthday she moved in with her father and stepmother. She married eight months later, when she was still only 16.

2. Cornelia de Kooning, born 20 July 1901 in Rotterdam, died 23 August 1901 in Rotterdam.
3. Adriana de Kooning, born 20 July 1901 in Rotterdam, died 7 August 1901 in Rotterdam.
4. Cornelia de Kooning, born 6 October 1902 in Rotterdam, died 11 June 1903 in Rotterdam.
5. Willem de Kooning, born 24 April 1904 in Rotterdam.

Leendert and Cornelia divorced on 7 June 1907.

Leendert married Neeltje Johanna Been, daughter of Hendrik Jan Been and Neeltje Johanna Derendorp, on 25 November 1908 in Rotterdam.Neeltje Johanna was born 31 May 1886 in Rotterdam.

Children of Leendert and Neeltje Johanna:

1. Neeltje Johanna de Kooning, born 21 September 1909 in Rotterdam. She married on 26 April 1933 in Rotterdam, probably with Gerrit J. Tamboer.
2. Leendert de Kooning, born 21 September 1909 in Rotterdam, died 24 September 1909 in Rotterdam.
3. Leendert de Kooning, born 2 April 1914 in Rotterdam. He married on 4 September 1935 in Rotterdam, but we don't know yet with whom.
4. Hendrika Johanna de Kooning, born 9 March 1918 in Rotterdam.

Cornelia Nobel married Jacobus Lassooy on 8 April 1908 in Rotterdam. Jacobus was born on 14 July 1875 in Rotterdam.

Child of Jacobus and Cornelia:

1. Jacobus Johannes Lassooy, born 8 May 1912 in Rotterdam.

Willem de Kooning, son of Cornelis (or Kornelis) de Kooning (or Koning) and Anna Catharina Jacoba Jurgens, was born on 24 November 1839 in Delfshaven, and died 6 February 1902 in Rotterdam.

He married Maria van Ladesteijn, daughter of Jacob Johannes van Ladesteijn and Gerarda van Essel, on 10 May 1865 in Rotterdam. She was born on 25 February 1843 in Rotterdam.

Maria seems to have been, or become, mentally deficient.

Children of Willem and Maria:

1. Gerardina de Kooning, born 5 February 1866 in Rotterdam. She married Gerardus Pieter Hogeweij, son of Gerrit Willem Hogeweij and Johanna Jacobs, on 13 May 1891 in Rotterdam.
2. Johanna Catharina (Jacoba) de Kooning, born 10 December 1867 in Rotterdam. She married Johan Samuel Willem Pflug, son of Nicolaas Pflug and Johanna Catharina van Leeuwen, on 15 May 1889 in Rotterdam.
3. Maria de Kooning, born 24 October 1869 in Rotterdam. She married Petrus Vrekke, son of Andreas Vrekke and Maragina Josina Hendriks, on 18 March 1891 in Rotterdam.
4. Cornelis de Kooning, born 4 October 1871 in Rotterdam. He married Wilhelmina Gijsberta Steegman, daughter of Hendrik Frederik Steegman and Wilhelmina van Wingerden, on 24 August 1904 in Rotterdam.
5. Cornelia Helena Rebekka de Kooning, born 3 November 1873 in Rotterdam.
6. Leendert de Kooning, born on 10 February 1876 in Rotterdam.
7. Willem de Kooning, born 29 January 1878 in Rotterdam. He married Maria Everdina van Keulen, daughter of Hendrik Willem van Keulen and Maria Lambregtse, on 18 September 1901 in Rotterdam.
8. Adriana de Kooning, born 28 March 1880 in Rotterdam. She married Antoon Pieter Homburg, son of Pieter Cornelis Homburg and Helena Kornelia Smits, on 7 August 1901 in Rotterdam.
9. Neeltje de Kooning, born 13 December 1881 in Rotterdam. She married Hendrikus Antonius Rotmeijer, son of Paulus Johannes Rotmeijer and Geertruida Hendrika Hoebe, on 17 September 1913 in Rotterdam.
10. Jacob Johannes de Kooning, born 1 April 1887 in Rotterdam.
11. Jacoba de Kooning, born 4 July 1884 in Rotterdam.

Christiaan Gerardus Nobel.

He married Cornelia Oers.