The child was found in a bathtub earlier Thursday afternoon at a condo in the area of Bathurst Street and Sheppard Avenue.
Police said the girl was found unconscious, choking on vomit, with shallow breathing. She was later rushed to North York General hospital without vital signs.
Police said the possible drowning appears to be accidental but an investigation is currently underway.
No charges have been laid so far.
The child's family does not live at the condo, and police said an adult woman was looking after the girl.
The babysitter had been looking after the child for the past year.
Pamela Fuselli of Parachute, an injury prevention organization, said that these kinds of fatalities are far too common.
"We see a couple hundred of these each year, of children drowning, about 10 to 15 per cent of those are in bathtubs," she said Thursday.