Montreal General hospital said 11 people had been admitted with bullet wounds on Wednesday, and eight were in critical condition. Some of the injured were taken to other hospitals in the area.
The assailant, who was described by witnesses as having a stone-cold face and wearing a trenchcoat, was killed by police.
Police confirmed on Thursday that the assailant was Kimveer Gill, a 25-year-old man from a Montreal suburb who referred to himself as the "angel of death" in his online journal.
Writing on one website where he called himself Trench, he said that he loved guns and hated people. Gill also posted several photographs on the internet showing him holding guns and hunting knives.
Police said 20 people were initially injured by Gill and later one of them, a 20-year-old woman, had died in hospital.
Michael Boyer, a student at Dawson college, told CBC Television: "We ran out of the building as a Swat team was coming in. They were screaming 'Where is he? Where is he?' And when you have 20 police running at you with guns, you really know that your life is in danger."
Witnesses reported that there was blood on the steps to the college, and inside the cafeteria, which is on the second-floor. They said at least 20 shots were fired.
One television image showed what appeared to be a body under a yellow covering.
Police have dismissed suggestions that race or terrorism played a role in the lunch-hour attack on Wednesday.
Students fled into the streets after the shooting began. Two nearby shopping centres and a daycare centre were also evacuated.
Dawson College is an English-language school with some 10,000 students between the ages of 16 and 19 in the heart of Montreal, Canada's second biggest city.
People fleeing the scene of the
school shooting in Montreal
The shooting triggered memories of the 1989 massacre at the Ecole Polytechnique de Montreal, where a man killed 14 women before killing himself.
Robert Soroka, a professor at Dawson College, said Wednesday's incident could have been a lot worse.
He said: "This could have been a very bad situation, if it had happened five minutes later when the students would have been exiting their classrooms during the changeover."