Byline: Ed Vulliamy

They gathered early, many with witches' hats or brandishing wands, still bleary from a late night listening to a band called Ministry of Magic.

The faux-baroque staircases and chandeliers of the Chicago Hilton are not accustomed to this type of client, strewn across the carpets eating pizza slices for breakfast and deciding whether to attend Evanna Lynch's yoga class or a discussion on "Making Harry Legit: Harry Potter Courses in College".

"Y'all make a lovely crowd," observed the muscular black security lady doubtfully, as Snape lookalikes and Ravenclaw robes rolled by.

It has been five years since the final Harry Potter book and a year since the denouement film, with JK Rowling's adult novel now eagerly awaited. But the afterlife of the epic series proliferates like an ever-expanding Hogwarts universe at the third LeakyCon, the global Potter convention named after the Leaky Cauldron pub in Diagon Alley. Five years since the publication of Deathly Hallows, the pilgrims have come in greater numbers than ever - 3,800 this year.

Those who jeer at Harry Potter as a fantastical celebration of toff-school traditions forget that this is not how books about wizardry and magic are viewed by young people - and their parents - in the stultifying, Bible-bashing suburbs of the American outback. There, for all the mass appeal of Hogwarts, the iconography and very notion of magic can be subversive and heretical.

"My parents aren't cool with it," says Caitlin R (Slytherin), aged 17, from Lincoln, Nebraska, with dyed red hair and wearing work boots. "It's just like a whole world they don't understand, and it scares them and they don't trust it."

Did they see the movies? "Yeah, they kinda liked Prisoner of Azkaban, but my interest in magic they don't like - or my tattoo." It's a circle and vertical line...