Ira Curry popped into the Georgia state's lottery headquarters holding her ticket with the lucky numbers eight, 14, 17, 20, 39 and Mega Ball seven.
"It's unreal. It's like I'm still dreaming," Curry, who lives in an Atlanta suburb, said in a statement issued by the Georgia Lottery.
The jackpot was $20 million shy of the record $656 million that was shared by three Mega Millions ticket holders in March 2012.
A state lottery official said Curry had used the birth dates of family members as the basis for selecting her winning numbers.
In lieu of an annuity, Curry opted for a single cash payout from the jackpot she'll share with a California ticket holder who has yet to come forward.
Mega Millions is sold in 43 of the 50 US states.
New rules went into effect in October that lowered the odds of winning to one in 259 million, but kept the price of tickets at one dollar each.