The ticket was sold at a store in Fountain Hills, Ariz., northeast of Phoenix.
Lottery officials during the news conference will not release the name or address of the winning family, Lottery Director Jeff HatchMiller said.
HatchMiller said officials will release information about the family's decision to play, when they bought the winning ticket and how they responded to discovering they'd won. They'll also release a statement from the family.
A Missouri mechanic and his wife, Mark and Cindy Hill, of Dearborn, Mo., already have claimed their half of the multistate Powerball prize.
The jackpot was the second-largest in U.S. history and set off a nationwide buying frenzy. At one point, tickets were selling at nearly 130,000 a minute.
Before the Nov. 28 drawing, the jackpot had rolled over 16 consecutive times without anyone hitting the jackpot. In a Mega Millions drawing in March, three ticket buyers shared a $656 million jackpot, the largest lottery payout of all time.