The Kapawe'no First Nation in northern Alberta Province said on Tuesday it identified 169 "potential" unmarked graves at site of the school, known as the Grouard Mission, about 370 kilometres northwest of Edmonton.
The school had been opened by the Catholic Church in 1894 and ran until 1961.
The findings came as a result of a six-day survey, conducted using ground-penetrating radar and drones, it said.
In a report posted on its website, the community said its findings are "the beginning of a long journey to find answers to what happened to the children who never came home from the residential school at St. Bernard's Mission."
"There remains a lack of justice and accountability for what happened," it said. "There is more work to be done to find those answers."
The latest discovery brings the total number of unmarked graves found so far to more than 1,500.
More investigations are also underway across the country into former residential schools, with more than 4,000 children believed to be missing.
The first such discovery occurred in May 2021 after an indigenous community unmarked a mass grave containing the remains of 215 children at the Kamloops Indian Residential School in British Columbia.
The incident prompted calls for justice and accountability for the victims and survivors of the residential school system, which forcibly separated indigenous children from their families between the late 1800s and 1990s.
Canada forced more than 150,000 Indigenous children to attend these government-funded compulsory boarding schools as part of a policy meant to assimilate indigenous children and destroy indigenous cultures and languages.
The children, who were stripped of their languages and culture, were also subjected to abuse, rape, and malnutrition. Thousands are believed to have died while attending those schools.
More than 130 residential schools were operated in Canada between 1874 and 1996.
A truth and reconciliation commission concluded in 2015 that abuses in the residential school system amounted to "cultural genocide."
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