Question: do muggles know about hogwarts?
Answer: A few things: In Goblet of Fire, Hermione explains that Muggles cannot see Hogwarts: '[Hogwarts is] bewitched,' said Hermione. ... Finally, Petunia managed to send a letter to Dumbledore when she was still a child (DH), so the barrier between the Muggle World and Hogwarts must have some flexibility.