Dirk IV was Count of Holland from 1039 to 1049. Dirk's date of birth is unknown but it was probably ca. 1030 or shortly before, he was described as "adolescent" at the time of his death. His base of operations was the stronghold his father built at Vlaardingen. Contemporary chroniclers referred to him as "Theodericus de Phlardirtinga" (Vlaardingen) and as margrave thereof. The exact extent of his domain is not known, but at one time or another it stretched north to at least Rijnsburg and east to roughly Aalburg.