[3] Quaker missionary work in the lower and middle Rhine River valley during the 1660s resulted in the conversion of a number of Mennonites in and around Krefeld.

In 1680, Herman and Hendrik Janez, two of that six exciled Quakers, published the pamphlet "Remonstrance" against Baron Kinski, the sheriff of the County of Moers, the Magistrate, inhabitants and the clergy of Krefeld.

[3] Afterwards they were eventually allowed to return through pressure from the English Quakers, but by this time William Penn's Colony was being established (1681–1682).

[4][5][6] The opportunity to follow their Quaker beliefs without fear of persecution was undoubtedly a major factor in their decision to emigrate from Krefeld.

[9] He continued his trade as linen weaver and remained prominent in Germantown civic and religious life.

In 1689 he was one of the eleven men to whom William Penn granted the charter of Germantown, where he was named as Hermann Isaacs opte Graef, towne President (a sort of burgomaster).

Penn directed Herman, his brother Derick and Thones Kunders to be the first burgesses,[3] and Abraham [Op den Graeff], with Jacob Isaacs Van Bebber, Johannes Kassel, Heifert Papen, Hermann Bon and Dirck Van Kolk to be the first committee-men.

[13] In 1691, Thomas Lloyd, Deputy General of Pennsylvania had granted a naturalisation to sixtytwo of the first Germantown settlers as citizens of Pennsylvania (and therefore of England) with the status of freeman including the three Op den Graeff brothers and also other important members of the settlement, Francis Daniel Pastorius and William Rittenhouse.

[14] The Krefeld Quaker advocates were Herman op den Graeff and his brother Abraham who sided Keith.

According to the book of June Shaull Lutz Herman had the following children from both of his marriages:[16] There is a reference about the Op den Graeff glass paintings of Krefeld with a description of Herman op den Graeffs coat of arms was found in the estate of W. Niepoth (op den Graeff folder) in the archives of the city of Krefeld, who noted a letter dated November 17, 1935 from Richard Wolfferts to Dr Risler: Saw the Coat of Arms glass pane in the old museum: 'Herman op den Graeff und Grietgen syn housfrau' or the like.