The Annalista Saxo records "duo fratres de loco qui Wimmeri dicitur in Thuringia, Willehelmus comes et Poppo ipsius cesaris capellanus", specifying that "frater vero illius Willelhelmus venerabili senectute vivens usque ad tempora Heinrici imperatoris de Bavenberch perduravit".
Graf im Helmegau 965. Graf im Altgau 967. Graf in Visichgau [Weimar] 974. He supported Heinrich "den Zänker" ex-Duke of Bavaria in his rebellion against Otto III King of Germany in 984. Duke in Thuringia 1002.
The necrology of Fulda records the death "1003 IX Kal Ian" of "Willehelmus com".
The name of Graf Wilhelm [II]'s wife is not known. Jackman suggests, for onomastic reasons only it appears, that she was --- von Grabfeld, daughter of Otto Graf von Grabfeld [Konradiner] & his wife ---. 1