One ticket sold at a Speedway gas station in Des Plaines, Illinois, matched the winning numbers of 13, 36, 45, 57, and 67, plus the Mega Ball of 14.
Illinois lottery officials said last-minute ticket sales upped the payout from $1.2 billion to $1.6 billion.
Illinois allows certain winners to remain anonymous. Monday, no winner had emerged. Lottery winners above $250,000 might request anonymity.