Recent research has shown that since the middle of the tenth century, the bishop of Utrecht had a leading role in the introduction and expansion of the parish system in the central Frisian districts east of the Vlie. In this study it is defended that he also played a significant role in Frisia between Vlie and Zonnemare, the area that since the late eleventh century was to be called Holland. Here as well, the demarcation of parishes and the establishment of ecclesiastical jurisdiction took place between 950 and 1025, a relatively short period which can nevertheless be regarded as formative, especially when one considers that, at the same time, the large-scale reclamation of the adjacent peatbogs began. Unlike in Central Frisia, where due to the lack of a strong comital power the bishop had to cooperate with local aristocrats, in Frisia between Vlie and Zonnemare the expansion of ecclesiastical power was realized with the support of the count, whose family appear to have had large estates at her disposal since the Viking period. This supports the assumption that despite a multitude of similarities between the Frisian areas on both sides of the Vlie, there were also fundamental and ancient differences, certainly with regard to the way in which regional power could be derived from land ownership.