Volunteers gathered Saturday at the Massachusetts National Cemetery in Bourne to place 77,000 flags on all of the graves for Memorial Day.
Paul Monti created Operation Flags for Vets back in 2011 to honor his son, SFC Jared Monti, who was killed in action in Afghanistan in 2006.
"They gave everything so that the rest of us could have the freedoms that we have," Monti said Saturday.
Jared was killed on his third attempt to rescue a fellow serviceman who was wounded. He was rewarded a Medal of Honor for his action.
It used to be illegal to plant American flags at veterans' graves. Monti spent more than four years pursuing a change of legislation to allow American flags to be planted on Memorial Day and Veterans Day.
"You know, it's actually growing," he said. "It's amazing that more and more people, it's becoming a tradition for many people. Entire families come down: grandparents, parents and kids. That's what makes me feel good is that we're passing it on down to generations."
Thousands of volunteers turned out for the event, including Gov. Charlie Baker.
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Diane Wersler, a volunteer at the event, said seeing people come together for a great cause makes her emotional.
Another volunteer, Jack Bernazzani, of Foxborough, echoed Wersler's appreciation for the event.
"When you've served, I think you know the sacrafice the people have made, and Memorial Day is to honor the sacrafice of those who died in battle," he said.
The ceremony began at 10 a.m. Saturday.
Monti expected about 5,000 people to help, including some World War II veterans in their 90s.
He says one of the hardest parts of about this day is placing a flag on his own son's grave.
"Rather he was placing a flag on my grave then me on his. Period."
Organizers are looking for volunteers to remove flags on June 3 at 10 a.m.