Harry's birthday is in July, which is the 7th month of the year
The Weasley family has 7 children
The Alohomora spell can be found in the Standard Books of Spells chapter 7
There are 7 Quidditch players in a team
Add the numbers of Platform 9 3/4 together ... 9+3+4 = 16, and 1+6=7!
There are 142 flights of stairs at Hogwarts which adds to 7 (1+4+2=7)
Gryffindor Tower is located on the 7th floor
Gryffindor hadn't won the house cup for seven years before Harry came
Nicholas Flamel and his wife have 7 years age difference
There are seven obstacles to obtaining the Sorcerer's Stone: Fluffy, Devil's Snare, flying keys, chess game, troll, potions, and the Mirror of Erised.
One of the obstacles that Harry and Hermione come across while trying to find the Sorcerer's Stone is seven
differently shaped bottles and a riddle.
Hogwarts students have to buy all 7 of Lockhart's books
There are 7 hidden passageways out of Hogwarts shown on the Marauders' Map
Flitwick's office (where Sirius is locked in the third book) is located on the 7th floor
There are 700 ways to commit a foul in Quidditch
Harry's Quiddich number is 7 in the POA film.
The Triwizard Tournament was first established 700 years before its appearance in the GOF
Fred and George charge 7 sickles for a canary cream
There are 7 locks in Moody's trunk
Moody was locked in the seventh lock of his trunk
In the American version of POA beginning Chapter 15, an illustration of Hagrid's letter to Hermione in regards to Buckbeak's trial shows 7 teardrops
Frank Bryce was said to be nearing his seventy-seventh birthday in GOF.
After the Weasleys, the Diggorys, Harry, and Hermione arrive with the Portkey to the Quiddich World Cup campground, a voice said, "Seven past five from Stoatshead Hill."
After hearing a loud, cracking noise while watching the news, Uncle Vernon waves from the window at "Mrs. Number Seven, who was glaring from behind her net curtains."
In OotP, during Harry's trial, Dumbledore states "...clause seven of the Decree [for the Reasonable Restriction of Underage Sorcery] states that magic may be used before Muggles in exceptional circumstances..."
Also in OotP, the boggart in the desk changes seven times to reflect Mrs. Weasley's worst fears: dead Ron, Bill, Mr. Weasley, Fred and George, Percy, and Harry
The Room of Requirement which is used for DA meetings is on the 7th floor
Lily began dating with James in their 7th year at Hogwarts
The prophecy is in row 97 in the Department of Mysteries
In OotP, when Harry fell down the stairs into the room with the veil, seven people came to his aid; Neville, Sirius, Lupin, Moody, Tonks, Kingsley, and Dumbledore.
Also in OotP, Harry and his group visit 7 rooms in the Department of Mysteries: the circular black room with the blue candles and many doors, the time room, the space room, the room with the veil, the Hall of Prophecy, the locked room, and the room with the brains.
In POA, when Snape is filling in for Professor Lupin, he instructs the class to turn to page 394. 3 + 9 + 4 = 16: 1+6 = 7. (also see "The Number 12" regarding this number)
There are 7 Animagi registered with the Improper Use of Magic Office
HBP came out on July 16, 2005 ... the month, date and year each add to 7!
In HBP, The Ministry of Magic sends out a purple leaflet with seven ways to protect the home and family against dark forces.
Harry and Ron both receive 7 O.W.L.s
In HPB Harry took up his position by his bedroom window, where he had been watching for Dumbledore since seven o'clock.
Blaise Zabini's mother is a famously beautiful witch who had been married (and widowed) seven times.
Harry takes the Half-Blood Prince's advice in his book to brew his Draught of Living Death and "...add a clockwise stir after every seventh counterclockwise stir."
Slughorn took the Felix Felicis potion for the second time in his life when he was fifty-seven.
While on his way to Dumbledore's office, Harry hides as Professor Trelawney passes by, shuffling dirty-looking playing cards. The second one she reads is the seven of spades - an ill omen.
Dumbledore's office is on the seventh floor of Hogwarts.
Quidditch practice is held at seven o'clock in the evening.
Six or seven Inferi crumpled when Harry hit them with the Petrificus Totalus spell.
Voldemort thinks 7 is the most powerfully magical number; therefore, Dumbledore believes that he divided his soul by 7: six Horcruxes and himself.
Contributing to this section: Monica, Serla, Christa, Dennis, Stephanie, Nolan, Kevin, bookworm, Annie, Cullen, Morgan, Brittany, Angelique, Brandi, M Strauss, Kathy, Estie, Dina, Ash, Bethany, Sese, Brittney, Julie ... and special thanks to Matt