The J. Renee touched down at 5:36 A.M. ET, according to spokesman Scott Lorenz. An initial search-and-rescue was requested before the balloonist was found to be safe.
Uliassi was reported to be in good condition, according to mission organizers.
A ground crew spokesman says they don't know why Uliassi landed. Their last communication with him had been 13 hours before he touched down.
Uliassi had faced a tough choice. Because crossing the Atlantic took longer than anticipated, he had to change altitude several times to avoid thunderstorms. Uliassi was unsure whether he had enough fuel and supplies to make it across the Pacific and finish the journey.
"In any long distance balloon flight there are several points where or a 'go' or 'no-go' decision has to be made," Lorenz said late Thursday. "It's water, water everywhere and it's several days without any land in sight."
Uliassi traveled more than 13,225 miles since launching from a rock quarry near Rockford Feb. 22.
Earlier this week, as his flight was crossing the coast of West Africa, Uliassi spoke on the phone with CBS Early Show Co-Anchor Jane Clayson, telling her, "The flight is going terrific."
The last time the 36-year-old balloonist described how, as he was flying over Puerto Rico and facing some serious thunderstorms. he wore his parachute, life raft and survival pack and stayed up for 28 hours until he was out of danger.
Then he experienced an interesting phenomenon.
"Sometimes sound can travel in strange ways. I could hear a guitar and a woman singing. I think I was 22,000 feet in the air, four miles up. I could hear it clearly."
Uliassi is 6'4" tall and finds conditions under the balloon "pretty cramped. Between me and all my stuff, there's barely room to sit down or lay down. If I had to do it again, I would make it a foot bigger in each direction," he said. The balloon is named the J. Renee, after his wife.
Closely watching Uliassi's progress was adventurer Steve Fossett, who holds the world solo balloon flight record - 14,235 miles - set in 1998. That trip ended when a storm off the Australian coast sent his balloon into the Pacific.
Speaking before the flight ended, Fossett said Uliassi could be proud of his attempt.
"I would think in Kevin's case that he has to be very pleased," Fossett said. "He's making one of the finest balloon flights ever, and he had not previously made a long balloon flight. It's outstanding so far."
Last March, Swiss psychiatrist Bertrand Piccard and English balloon instructor Brian Jones became the first to circle the world nonstop in a hot-air balloon, landing safely in Egypt.
To ount as an around-the-world flight, a balloon must cross all lines of longitude and must cover at least half the length of the equator, according to the Federation Aeronautique Internationale, the governing body of air sports.
The distance around the globe at the equator is 24,902 miles.