At the largest Barnes & Noble bookstore in Orlando, the cartons of books remain behind a padlocked door, and won't be opened until just before midnight, reports CBS News Correspondent Peter King.
It may be a bigger deal than Hillary Clinton's book.
"I would say this is probably one of the biggest book events we've seen in years," said B&N Orlando's Seth Brandler.
"All the stores have special crafts planned, and activities for the kids," he said. "In our store alone, we're doing a costume contest and we're going to have a special story time.
At the Borders bookstore in Bowie, Md., eager fans will get an advance preview at 10 p.m. with a reading of the book's first chapter.
Changing Hands in Tempe, Ariz., will offer Renaissance Festival jesters, jugglers and crooners strolling the aisles beginning at 10 p.m. They'll be joined Saturday by owls from the Phoenix Zoo.
Publisher Scholastic has printed ordered a record 8½ million copies of the book, which comes nearly three years after the last book in the series.
Associated Press reviewer Deepti Hajela says "it was worth the wait. And then some."
Readers will see a different Harry Potter in "Order of the Phoenix," reports CBS News Correspondent Charles D'Agata in London. He's 15 now, facing girl trouble, hormones, the death of a loved one, and, says author JK Rowling.
"He's a lot, lot, angrier in this book, and justifiably so," she said.
She also said Harry starts his first "a relationship ... of sorts."
Everything is bigger in this fifth book, starting with the number of pages — the 870-page tome is by far the longest of the series. At this rate, the seventh book might have to be published in two volumes.
At the end of the fourth book, Harry had narrowly escaped from Voldemort, who regained the powers he lost when he tried to kill the boy all those years ago. Harry and his friends want to warn the wizarding world of the danger, but the powers-that-be don't want to hear it.
This fifth book opens about a month later, with Harry back among non-magical folk, desperate for any news about what Voldemort is up to. He's frustrated by the lack of information from his wizard friends, wondering if they're aren't telling him anything because they don't have faith in him.
As the latest adventure tale of the young wizard hits the stores, retailers hope to sell more than just books.
Wal-Mart Stores Inc. will offer Harry Potter cakes and is increasing its selection of toys and DVDs. Toys "R" Us has created Harry Potter boutiques within its stores.
But the popularity of these items, which are not tied to the new title, "Harry Potter and the Order of the Phoenix," remains to be seen, because books generally don't move merchandise the way movies do.
"I never believed that Harry Potter in its literary form is an engine for merchandise sales," said Seth Siegel, co-owner of The Beanstalk Group, a trademark licensing group.