Jim Wilson II, 84, and his wife, Shirley, 79, claimed the winning prize from last Wednesday's drawing, along with their three sons.
"I was absolutely astonished," said Jim Wilson, a retired electrician who served in the Army's 82nd Airborne Division in Africa and Europe, at an afternoon news conference. "I couldn't believe it, and still don't."
He bought the winning ticket — with the numbers 9-19-29-42-53 and a Powerball number of 17 — at a grocery store in St. Louis County. The store will get $50,000.
When the Wilsons learned they had won, they got professional financial advice before claiming the prize.
Jim Wilson II has the option of receiving $254 million in 30 payments over 29 years, or accepting a lump-sum payment worth $120 million before taxes.
The couple said they will share the money with their sons. The St. Louis family has been buying family Powerball tickets for years with the understanding that they'd share any winnings, the Missouri Lottery said.
Two sons — Bill, 54, and Jim III, 59 — lost their jobs in the past year, though Bill Wilson has found a new one. Another son, Terry, 53, said he hasn't had a vacation in 30 years and will probably go to Australia.
The couple also said they will set aside money for their grandchildren and great-grandchildren.
The Wilsons' prize is the 10th-largest single-ticket lottery prize in world history, with all 10 coming from the United States, Missouri Lottery officials said. The largest was a $365 million prize won by eight Nebraska meatpacking plant workers in February 2006.