Three US marines killed in a Northern Territory military aircraft crash last year have been honoured at a Tiwi and Larrakia healing ceremony in Darwin, where their families were formally adopted by Tiwi leaders.

In August last year, an MV-22B Osprey carrying 23 US marines crashed on Melville Island, one of the two Tiwi Islands north of Darwin, during routine training for Exercise Predator's Run. 

Captain Eleanor LeBeau, 29, Corporal Spencer Collart, 21, and Major Tobin Lewis, 37, were killed in the crash.

More than a year later, on Thursday, the US marines and their families were honoured in a series of ceremonies in Darwin attended by hundreds of people.

The families, and members of the US Marine Rotational Force — Darwin, were welcomed with a Larrakia smoking ceremony, and adopted by Tiwi leaders, on whose homelands the crash occurred.

Tiwi-Mantiyupwi leader Jennifer Ullungura Clancy said the crash had left the Tiwi people grieving for the loss of life on their country.

"The day it happened, it was very hard for my people to move on, to be happy the next day," she said.

"We can do [ceremony] and grieve our own way, to let go."

Ms Ullungura said it was important for the American families to be adopted by Tiwi people.

"When they come, they can do their grieving on their own, and then we do it together as one," she said.

David Kurnoth was among the Larrakia representatives who performed a smoking and healing ceremony for those who gathered.

He said the ceremony was performed because the marines on the Osprey had slept on Larrakia country the night before their last mission. 

"There are certain guidelines and certain rules that we adhere to, and in today's world it's a little difficult to do that," he said.

"But thankfully, opportunities like this arise so that we can do it properly and do it right."

Spencer Collart's parents Bart and Alexia Collart were among those at the ceremony.

They described Spencer as a loving son who enjoyed sports, video games and the time he spent in Australia.

"He loved everything about Australia. I think maybe he might've moved here if he had his choice," Alexia Collart said.

She said their family's adoption and naming by the Mantiyupwi clan was especially meaningful because the couple had themselves adopted Spencer and his sister as one-year-olds.

"They're our true children and we love them so so much," she said.

"We're a very close-knit family, and clearly the Tiwi people are about family too, so that's what really draws us to them, and we feel one with them."

"Our marine corp family has been wonderful as well, and it's just an honour to be here," Bart Collart said.

The families will on Friday travel to the Tiwi Islands for a second, private memorial.