(July, Harry Potter, Harry, Potter) The day of Harry Potter's birth.

Source:

The date - The letter from Hogwarts in Book 1.

The year - In book 2 Nearly-Headless Nick celebrated his 500th Deathday; we know he died on October 31st, 1492, making the date of the party October 31st, 1992. Harry was 12 in Book 2, so 1992 - 12 = 1980).