Gerolf or Gerulf was the second count of this name who is attested in the area of Friesland (which also included Holland at the time). Gerolf's main area of power seems to have been in Kennemerland. Gerolf acquired Teisterbant. Count Gerolf is often regarded as the founder of the County of Holland, although the actual name "Holland" is from a later time. The first house of the Counts of Holland ruled the county until it was inherited by John II of Hainaut in 1299. His ancestry is unclear, but he may have been a son or, more likely, a grandson of the earlier Gerolf, who was a count in the area of Frisia at the time of the reign of Emperor Louis the Pious (778-840) and who later joined a monastery. The earlier Gerolf died in 855. There is some limited and vague evidence that this earlier Gerolf was a son of a certain Theodoric, who in turn supposedly descended from the Frisian king Redbad (d. 719). Count Gerolf is often identified as the father of Dirk I, the second count of Holland, but Dirk may well have been his adoptive son. Waldger, Dirk's elder brother, inherited the County of Teisterbant.
| Count of Kennemerland