He was 27 days younger than the world's oldest person, Besse Cooper.
Mr Breuning had lived at the Rainbow Senior Living retirement home since 1980 and attributed his long life to eating only two meals a day for the past 35 years.
In an interview last year, he also attributed his longevity to 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.
Democratic governor of Montana, Brian Schweitzer, said: "I am deeply saddened by the loss of my dear friend and a great Montanan.
"Walter taught me that all things in moderation will help lead to a long life; that hard work and a modest living are enough for a happy life and most importantly that giving back to others is good for the soul."
Born in the town of Melrose, Minnesota, on September 21, 1896, Mr Breuning moved to Great Falls in 1918, where he found work with Great Northern Railway and remained there for 50 years.

He married co-worker Agnes Twokey, who died in 1957 after 35 years of marriage. The couple did not have any children and Mr Breuning never remarried.
Retiring in 1963, aged 67, he stuck to his philosophy and continued to work as a manager and secretary for Shriners, a position he held until he was 99 years old.
In recent years, Mr Breuning also attracted a following, appearing on News Hour with Jim Lehrer in 2009 and participating in a question-and-answer segment in the magazine Men's Journal.
He was officially listed in the Guinness Book of World Records 2011 edition as the world's oldest living man.
He had inherited the title from England's Henry Allingham, who passed away at the age of 113 in July 2009.

Source : Yahoo