Police, who confirmed no one in the house survived, hadn't released the names of the victims of the fire in the two-story brick home in East Gwillimbury, north of Newmarket, the Toronto Sun reported.
"They were honestly just the best family. I can't even begin to explain how many people are devastated over this," Ashley Bailey, a 16-year-old neighbor, said.
Constable Blair McQuillan told the Sun an emergency call was placed from in the home about 5:30 a.m.
"Police were the first to arrive on scene," he said. "The home was on fire and the four occupants in a room at the front of the house were unable to get out."
East Gwillimbury Mayor Virginia Hackson said the tragic fire would deeply affect the tight-knit community, Toronto TV station CityNews reported.
"It's a very difficult day for us as we mourn the loss of four residents," she said. "It's a very sad day."
The TV station said a neighbor said a fifth member of the family was away at college.
The cause of the fire hadn't been determined.