A mais antiga menção está em Harry Potter e a Pedra Filosofal Capítulo 5: Beco Diagonal.
‘What sort of magic do you teach, Professor Quirrell?’ ‘D-Defence Against the D-D-Dark Arts,’ muttered Professor Quirrell, as though he’d rather not think about it. ‘N-not that you n-need it, eh, P-P-Potter?’ He laughed nervously. ‘You’ll be g-getting all your equipment, I suppose? I’ve g-got to p-pick up a new b-book on vampires, m-myself.’ He looked terrified at the very thought.
Nós aprendemos no Capítulo 3 de Harry Potter e o Prisioneiro de Azkaban que Harry viu uma foto de um vampiro em sua classe DADA.
Harry looked into the shadowed eyes of Sirius Black, the only part of the sunken face that seemed alive. Harry had never met a vampire, but he had seen pictures of them in his Defence Against the Dark Arts classes, and Black, with his waxy white skin, looked just like one.
Como você diz, a primeira vez que ele encontra um deles é na HP e no Enigma do Príncipe