According to De Villiers/Pama, the genealogy of the Du Plooy family in South Africa starts with Symon Ploijer ( a.k.a. Simon du Plooy), of Krommenie in North-Holland, bapt. 1666, died 1733. He was first married to  Adriaantje, (parents unknown) and secondly to Catharina Koopman, parents also unknown.

4.  Symon Pieterszoon PLOIJER, or
     Simon Pieters DU PLOOY

He was baptised at Krommenie 29 Augustus 1666. On 22.9.1715 he married Catharina Koopman, his second wife and our ancestress. At that time his age was 49. 

DeVilliers/Pama states that Simon's first child was a son: Pieter Simon.  No dates are given. This Pieter was probably the son of Adriaantje, Simon's first wife, because the second child, Willem, was baptised on 5 Januarie 1716,four months after the marriage to Catharina.

DeVilliers: "Geslachtregsiters van de Oude Kaapse Familiën"  gives Simon's children as follows: 

5. Cornelis DU PLOOY: bapt 1 February 1744. He was a citizen of Stellenbosch and married  Margaretha WILLEMSE 17 April 1768.

His second wife was Anna Sophia CAMPHER, whom he married 24 August 1788, when he was 44 and she was 19 years old.

Cornelis DU PLOOY had 19 children, eight by his first wife, Margaretha, and eleven by Anna Sophia CAMPHER.

Cornelis's ninth child and Anna Sophia's eldest, was our ancestor:

6. Dirk Wouter DU PLOOY: bapt. 6 Desember 1789 at Swellendam. He lived at Uitkyk, in the Gamka district of Beaufort. He was a Voortrekker and probably left the Colony in Julie 1837 with the party of Jacob de Klerk. He was present at the Battle of Blood River, and later settled in the Hopetown District, where he died 27 October 1868 on the farm Maartenspan.                                                  (Source: J.C. Visagie: Voortrekker Stamouers, page 62)

Dirk Wouter married Catharina Susanna ROUX, a daughter of Pieter Hendrik ROUX and Elizabeth STEENBERG. She was born 31 July 1796 in Tulbagh, and died at Maartenspan, Hopetown, 23 October 1868, four days before her husband. (Why? What happened? There's a story here, if only we knew it!)

Dirk Wouter and Catharina had 4 children: 

1. Cornelis Willem, born 21 December 1813, Beaufort-Wes (our ancestor)

2. Pieter Hendrik Rudolf, born  5 December 1816, Beaufort-Wes

3. Catharina Susanna Petronella, born 28 Jan 1821, Beaufort-Wes

4. Willem Andries, born  22 Feb 1823, Beaufort-Wes

7. Cornelis Willem DU PLOOY:  born  21 December 1813
in Beaufort-Wes, baptised 13 Feb 1814 Graaff-Reinet.

On 3 Februarie 1837, when he was 24 years old, he was offered the appoinment of field cornet for the Gamka District. He turned it down because he was about to leave the Colony. He left in July 1837, joining the trek of Jacob de Klerk. Hy was probably the "Willem du Plooy" who was present at the Battle of Blood River.          
                                           (Voortrekker Stamouers - J C Visagie, page 61.)

On 3 July 1837 at Beaufort-Wes he married Johanna Marguerite Jacoba Susara NEL, born 13 December 1820: a daughter of Jacobus Frederick NEL and Maria Johanna WILKERS. The bride was 17 years old. 

He died on 2 June 1881 at Maartenspan, Hopetown, at the age of 68.

Cornelis Willem DU PLOOY and Johanna M.J.S. NEL had eleven children: 6 sons and 5 daughters.The third child and second son,  Jacobus Frederick, is our ancestor.

8. Jacobus Frederick DU PLOOY: born 29 July 1843, baptised 2 October 1843 at Colesberg. He married Cornelia Carolina DU PRE. Their children were:

1. Cornelis Willem born about 1870 at Hopetown.

2. Jacobus Frederick

3. Rudolph

It is possible that there were more children, but we don't know of any.

Cornelis Willem is our Oupa Neels who married Ouma Annie de Villiers.