DEFOREST, Wis. -

Hundreds gathered on Monday in DeForest for a special Memorial Day tradition that began as a way to honor a local U.S. Marine who was killed while serving overseas.

Memorial Day has become a very special tradition for local mother Peg O' Donnell and her adopted "Marine family." It has been more than seven years since her son, Lance Cp,. Shane O'Donnell was killed in Iraq in 2004.

Every year since her son's death, Peg O'Donnell said she and her Marine family have gathered at the DeForest Memorial Day ceremony. She then hosts lunch for them. Some years, up to 40 Marines and their families attend to remember their fallen friends. All are part of her son's group, G Company.

Scott Kruchten, who served with Shane O'Donnell, said that the event highlights the closeness the group members have developed.

"Peg really learned what Marine Corps family is all about," he said. "We've gone from kind of being her Marine Corps family, adopted, to being her family. And that's what family's for is support."

She said it's become an important occasion.

"Shane might not be there, but that closeness is. And I know if I dialed the phone, 24-7, it doesn't matter, and need something, one of them will be there," she said.

The year after her Shane's death, a tree was planted in his honor at Veterans' Park in DeForest.

Peg O'Donnell said when her Marine family found out about the tree, they came for the first Memorial Day ceremony to honor it, and they just keep coming back.

"They just kept coming back. They're cool," she said. "They're family -- they really are."

After lunch, Peg O'Donnell and the Marines always head to the G Company ceremony, where they honor her son and the four other G Company Marines who were killed while serving in Iraq.

For Peg, the importance of this tradition is the sense of having her son's friends around her. She said she thinks her son would have loved it.

"It's the camaraderie, and knowing that they're always there -- the wives, the kids, all of them," she said. "We see each other a couple times a year, and this is one of those times. It gives me goose bumps because they rock!"

For many, the group's tradition sums up what Memorial Day is all about: Honoring fallen heroes and getting together with love ones to remember them and their sacrifice.