"Idaho is a very lucky place," state lottery director Jeff Anderson said. "We are encouraging everyone who has played Mega Millions to check their tickets carefully for winners."
The odds of having the winning numbers in Tuesday night's drawing were one in 176 million.
When the Idaho winner comes forward, they can elect to take a lump sum option of about $81 million after state and federal taxes, lottery officials said.
Though the top winner has not come forward, Idaho is home to another big winner. Kevin Anderson of Melba, Idaho, had five of the six numbers on his ticket, so he'll get $250,000 before taxes. He had been out of work for two years but recently got a new job.
He said he considered the win an early birthday present. He'll be 50 Jan. 25.
"We danced for the next 20 minutes," Anderson said when he claimed his prize. "I needed another number to quit my job."
After taxes, he walked out of Idaho Lottery headquarters with a check for $168,000, money he said he and his wife mostly would save and maybe use to buy a new car.
The family struggled with finances and "couldn't afford Christmas, so this is just perfect," he said.
Lottery director Jeff Anderson said, "We are also recommending all our players sign the back of their tickets prior to presenting it for payment. These tickets are bearer instruments, and we want to ensure our winners protect their play."
Mega Millions is played in 41 states, the District of Columbia and the U.S. Virgin Islands.
The jackpot grew to $355 million because Friday night's drawing failed to produce a winner for the multi-state lottery's top prize, which was estimated to be $290 million.
On Wednesday, lottery officials increased the jackpot estimate to $380 million after a boost in last-minute ticket sales.
The jackpot grew to such "mega" dimensions after 15 consecutive drawings that started Nov. 12.
Mega Millions jackpots begin with $12 million and roll over to the next drawing until there is a winner.
The Mega Millions lucky numbers were eerily similar to the ones that haunted fans of the ABC television series "Lost" for six seasons.
The numbers the character of Hugo "Hurley" Reyes used to win $156 million were: 4, 8, 15, 16, 23 and 42, four out of the six numbers picked on Tuesday.
On the show, Hurley, played by actor Jorge Garcia, thought the numbers were cursed after suffering a string of bad luck after winning the lottery on the show.
Though Hurley may have been unlucky on "Lost," someone playing his numbers in Tuesday night's drawing would have won $150.
"Lost" co-creator and executive producer Damon Lindelof said the coincidence might be good karma for the show's dedicated fans.
"Considering the show pretty much drove its fans crazy for six years, it seems only karmically just that it has finally decided to give back," Lindelof told ABC News.
Fellow executive producer Carlton Cuse said via Twitter not to blame the show's creators if the lottery connection, like many of "Lost's" plot twists and turns, remained unsolved.
"I'm sure there is a larger, mystical reason this happened, but in this case if it never gets explained, don't blame me or Damon," he wrote.
ABC News' Steve Osunsami, Michael S. James, Kevin Dolak, John Griffin, Jennifer Metz and The Associated Press contributed to this story.