Note: the following is an excerpt from the writings of Bartus Willem Kapteyn. These notes are only his opinion, and have no basis in confirmed fact. Another story is that two Huguenot Capitein brothers from the Burgundy region of France came to the Netherlands to escape persecution from predominantly catholic France, and most of the Kapteyns come from these two. However, I felt Bartus' notes were still interesting, so I am including them here.
They are as follows:
The first known documents of the Kapteyn family point in the direction of the village of Berkoude or Berkenwoude in the Krimpenerwaard in the Netherlands. Berkenwoude as we find it on today's map is located between Gouda (NW), Stolwijk and Zuidbroek (NE), and Lekkerkerk (S) and Krimpen (SW).
The Krimpenerwaard is one of the "Waarden" which are bordered by the great rivers that run through this area; the Lek, the Hollandse Ijssel, and the Maas. People of this area are known to be very religeous and often on the heavy and sombre side of it.
The farmers have the added difficult task of defending the land against the water of the rivers. The dikes around the rivers of the Krimpenerwaard are known to have existed already in the year 1097.
Krimpenerwaard is the "Waard" in Zuid-Holland located west of the Lopikerwaard and enclosed by the Lek, the Maas, and the Hollands Ijssel, mainly consisting of peat-bog, with riverclay along the rivers. It is a separate unit of dike-control government. It includes the municipalities of Krimpen aan de Ijssel, Krimpen aan de Lek, Lekkerkerk, Oudekerk aan de Ijssel, Berkenwoude, ("Berkouw"), Gouderak, Stolwijk, ("Stolk"), Bergambacht, Ammerstol, Haastrecht, Vlist, and Schoonhoven. The dikes are very old; in a charter of Count Floris de Vette (The Fat One) of 1097 already rules were made for the maintaining of the dike. The soil is mostly occupied by grassland. The main sources of the means of support are the keeping of cattle, beef, and pigfarms, and the making of cheese at the farms.
The name Kapteyn appears much later. One of the first known forebears must have had the name Pouwel or Pauwel. He was born circa 1538. Some documents of the year 1543 indicate that people by the name of Pauwels had some properties in the area of Berkou.
About his son we know little more than the name, Cornelis, born 1568.
The next generation is Pouwel Cornelisz born in 1605, died in 1651.
Note: Since children were often named after the grandparents, we can conclude that the grandfather's name of Pouwel Cornelisz was Pouwel. Since a generation is calculated at circa 30 years we may assume that the grandfather of Pouwel Cornelisz was Pouwel, born circa 1538.