The short answer: ticket sales.
"For each ticket sold, a portion is put into the jackpot fund. If there is a winner in an early jackpot, where sales may not be enough to cover the jackpot amount, each state contributes a share, based on their sales percentage, to make up the difference," Elkin says.
For Mega Millions, the jackpot starts at $40 million and rolls over until someone wins.
The values of the current Mega Millions prizes are based on sales through 10:45 p.m. ET on Tuesday, so the exact amounts are still being tallied, the lottery said Wednesday.
About half of the profit from the $2 tickets goes towards the prizes, according to a Mega Millions spokeswoman, and the rest of the proceeds are distributed to the 44 participating states, plus D.C. and the U.S. Virgin Islands. The money goes to pay for states' retailer commissions, administrative fees and the good causes supported by the lotteries, including education.
Individual states determine specifically how the lottery revenues are allocated. For example, Ohio lottery ticket sales have contributed over $24 billion to education since 1974. Ticket proceeds in Colorado, meanwhile, go to Great Outdoors Colorado, which funds preservation efforts around the state's parks, trails and wildlife.