The Navajo Nation Council confirmed his death, hailing the services and sacrifices made by Navajo warriors.
Kellwood died Monday at the Veterans Hospital in Phoenix, according to an obituary
posted at a local mortuary. He served in the First Marine Division and fought during World War II in the Pacific front, seeing battle in Cape Gloucester, Peleliu and Okinawa.
As a boy, Kellwood had been spanked in school for daring to speak Navajo. But his language skills would later prove indispensable in US war efforts.
The Marines tweeted a video of Kellwood singing the Marines' hymn in Navajo and wrote: "Honor the fallen. Yesterday, one of the last remaining Navajo code talkers passed away at 95 years old."
The Navajo Times reported earlier this year that there are less than 20 surviving code talkers
Kellwood worked as a Navajo code talker until the war ended in 1945. He was awarded the Congressional Silver Medal, Presidential Unit Citation, Combat Action Ribbon, Naval Unit Commendation, Good Conduct, American Campaign Medal, Asiatic-Pacific Campaign Medal and WWII Victory Medal, according to his obituary.
The Arizona governor called Kellwood a "hero and patriot."
"Kellwood served with distinction in the 1st Marine Division as a Navajo code talker, ultimately helping lead the allied forces to victory in World War II," Gov. Doug Ducey said in a statement. "Let us never forget the countless contributions that code talkers made to our state and our country."
Longed to join the Marines
Kellwood was born in Steamboat Canyon, Arizona, in August 20, 1921.
When he was 10, he was sent to a school at an Apache reservation run by the US military, he told the Veterans History Project in an interview.
He couldn't speak English so he got punished when he spoke in his native language.
During World War II, he wanted to enlist in the Marine Corps after reading about efforts in the Battle of Guadalcanal, he told the Veterans History Project. He had no idea about the code talkers when he enlisted in 1942, since it was a secret program.
The Navajo code talkers trained at Camp Elliott, near San Diego. Kellwood underwent intensive training, learning Morse code, radio and Navajo codes.
"I studied on my own at night," he said about the training. "You had to memorize all the words at the time, 211 words. They were long words. I spelled it. I learned."
Military authorities chose Navajo as a code language because its syntax and tonal qualities were almost impossible for a non-Navajo to learn, and it had no written form. The ranks of the Navajo code talkers swelled to more than 300 by the end of the war in 1945.
The code talkers were involved in transmitting tactical information in every major operation involving the Marines in the Pacific, according to the CIA.
The Navajo code baffled the Japanese, who had successfully deciphered codes used by the US Army. After the war, the Japanese chief of intelligence, Lt. Gen. Seizo Arisue, admitted they were never able to crack the Navajo code used by the Marines and Navy, according to the Navy
The code talkers were forbidden from telling anyone about it until their work was declassified in 1968.
The group later gained legendary status with books and, ultimately, a 2002 movie that was inspired by their stories called "Windtalkers," starring Adam Beach and Nicolas Cage. .
Brothers die within days of each other
After the war, Kellwood settled in Sunnyslope, Arizona.
He was close to his older brother, Roy Kellwood, who was also a World War II veteran and had served in the US Army Air Forces in Europe. They were always sharing stories and checking up on each other, said nephew, Roy Kellwood Jr.
Kellwood passed away just three days after his older brother died at age 101.
"They were Navajo warriors -- that's what everyone calls them," said Roy Kellwood Jr.. "They defended the country, not just for the US, but for the Navajo nation and the Navajo people."
Their funerals will be held at the same time, he added.
Joe Kellwood will be buried at the National Memorial Cemetery of Arizona on Thursday.
"We all have wonderful memories of seeing his face light up when we walked into the room," according to an obituary posted by his family.
"He loved to tell funny stories, laugh out loud and say 'by golly.'"