Buchanan suffered a stroke the day before Thanksgiving and died Wednesday, said Marge Schwendenman, executive director of the assisted living facility where Buchanan spent his last two years.
"He was the last of the gentlemen," Schwendenman said. "He always tipped his cap, always let ladies go first in the elevator. Everyone just loved Russell. We all have a tear in our eye today, but we're celebrating his life."
There are 14 confirmed World War I veterans still alive in the United States, said Terry Jemison of the federal Veterans Affairs Administration.
Buchanan served in the Navy in the final months of World War I and then enlisted in the Army to serve in World War II when he was in his 40s.
He remained physically active in his old age, regularly walking at a local shopping mall well past his 100th birthday. He participated in a Veterans Day event at the Massachusetts Statehouse last month, Schwendenman said.
Buchanan at first tried to join the Marines but was turned down, he told The Boston Globe newspaper in a 2001 interview. He was allowed to join the Navy in 1918 only after gaining a few pounds (kilos) to make the 118-pound (53-kilogram) minimum.
After joining the Army in 1940, he was sent to Europe.
"Stand up for the U.S.A. and give all you can, even if it hurts," Buchanan said at a Veterans Day ceremony in 2001.