Breuning died of natural causes in a Great Falls hospital, said Stacia Kirby, spokeswoman of the Rainbow Senior Living retirement home where he lived. Breuning had been hospitalized since the beginning of the month with an undisclosed illness.
Breuning was 26 days younger than Besse Cooper of Georgia, whom the Gerontology Research Group in Los Angeles lists as the world's oldest person at 114.
In an interview with The Associated Press last fall, Breuning attributed his longevity to eating just two meals a day, working as long as he could and always embracing change - especially death.
"We're all going to die. Some people are scared of dying. Never be afraid to die. Because you're born to die," he said.
Breuning was born on Sept. 21, 1896, in Melrose, Minn., and spent his early years in De Smet, S.D. That first decade of the 1900s was literally a dark age for his family. They had no electricity or running water. A bath for young Walter would require his mother to fetch water from the well outside and heat it on the coal-burning stove.
He lied about his age and got a job in Minnesota with the Great Northern Railway in 1916 at age 16. He moved to Great Falls two years later and remained a loyal railroad man for the rest of his life, working there for 50 years, marrying co-worker Agnes Twokey and traveling by airplane only once in his life.
He earned $90 a month for working seven days a week at the beginning, and amount that he said was "a lot of money at that time."
In 1919, he bought his first car, a $150 secondhand Ford. Breuning remembered driving around town and spooking the horses that still crowded the dirt streets of Great Falls.
"We had more damn runaways back in those days," Breuning said. "Horses are just scared of cars."
He and his wife bought property for $15 and planned to build a house, but it all went off the tracks when the Great Depression struck.
"Everybody got laid off in the `30s," Breuning said. "Nobody had any money at all. In 1933, they built the civic center over here. Sixty-five cents an hour, you know. That was the wage - big wage."
Breuning was able to hold onto his job, but he and Agnes never built their house. They sold the lot for $25, making a tidy $10 profit. It turned out to be the only time Breuning ever owned property - he was a renter for the rest of his life.
Agnes died in 1957 after 35 years of marriage. The couple didn't have any children, and Breuning never remarried.
In 1963 - the year the Beatles released their first album - Breuning decided it was time to retire at age 67.
But he stuck by his philosophy and kept working. He became the manager and secretary for the Shriners, a position he held until he was 99.
Breuning moved into the Rainbow Retirement Community since 1980, calling home a spare studio apartment with bare walls.
Breuning would spent his days in an armchair outside the retirement home director's office in a suit and tie, sitting near a framed Guinness certificate proclaiming him the world's oldest man. He would eat breakfast and lunch and then retire to his room in the early afternoon. He'd visit the doctor just twice a year for checkups and the only medication he would take was aspirin, director Tina Bundtrock said.
With most of his relatives gone, Breuning said his real family was there in the Rainbow. He received letters from admirers from around the world, and he kept up with world events.
"Everybody says your mind is the most important thing about your body. Your mind and your body. You keep both busy, and by God you'll be here a long time," Breuning said.
Breuning had requested no funeral services, retirement home officials said. He asked that donations to the Shriner's Children's Travel Fund and the Scottish Rite Language disorder Center be made in lieu of flowers and cards.