Willem Gerretse Kouwenhoven resided at first in Brooklyn, of which place he was a magistrate in 1661, '62 and '64. On the earliest surviving lists off the Reformed Dutch Church of Brooklyn, Sept. 12, 1660 appear the names of Willem Gerretse Van Couwenhoven and his first wife and her parents. He was a deacon in that church in 1663. Signed a petition as a schepen of Brooklyn on May 25, 1662. From thence he appears to have removed to Flatlands, his name appearing on the patent of said town of 1667; on its assessment rolls of 1675, 83, and 93; elder of its Reformed Dutch Church in 1677; and taking the oath of allegiance there between Sept. 16-30, 1687 being called a resident of "fflackland" and native-born. November 1, 1709, he sold his Flatlands farm to his son William (see Lib 5, page 30, of Con.) and (sup) in 1727 he removed to Monmouth Co., NJ. Died abt 1728 and apparently certainly after 1727. James Riker in his Annals of Newtown in Queens County, NY, says he was "living in 1727 at a very advanced age. The records of the Brick Church, Marlborogh, Monmouth Co., NJ originally knowwn as the Reformed Church of Freehold of the Navasink, begin in 1709 and show that in that year seven children of Willem Gerretse were already members of that congregation, namely, Cornelis, Pieter, Albert, Jan, Jacob, Neeltje (Nelke) and Sara. In 1717 appear as members two other children, Annetje (Autie) and Jacobina (Jockamiinke). It was not until 1721 that the church shows as members "Willim Ger Kowvenhoven and his wife".and since the wife, Jannetje (Janneke), appears alone on the list in 1723, it seems possible that Willem Gerretse died between 1721 and 1723.
Willem Gerrets, on behalf of his first wife, was one of the three heirs to the Brooklyn grant of hi father-in-law, Joris Dircksen Brinckerhoff, and joined with the other heirs in selling this property on January 16, 1661.
The existence of the original bible of Willem Gerretse, with his own record of his marriages and the births of his children, greatly assists in determining his twleve children. He states that he married "Altieu Yoris" in the year 1660. She was Altje, daughter of Joris Dircksen Brinkcheroff, and was the widow of Cornelis Mattys (Matthews). She died on June 3, 1663 and Willem Gerretse married, secondly, on February 12, 1665, "Jannetie Peters", who was Jannetje, daughter of Peter Monfort. She was baptised as Jaannetje on May 8, 1646, in the Dutch Reformed Church of New Amsterdam.