The Special Investigations Unit said the incident under investigation occurred in the Thomas Street and Erin Mills Parkway area in the early hours of Aug. 28.
Their preliminary information indicates that Peel Regional Police had received calls about a woman walking along the road.
The SIU said that police spoke with the woman and "at some point" a Taser was deployed and the woman fell to the ground.
The woman was taken to Credit Valley Hospital where she was treated for injuries that included a broken hip.
The SIU has identified one subject officer and two witness officers.
The SIU investigates all incidents involving police in which death or serious injury occur, or when allegations of sexual assault are raised.
Ontario recently announced that it would allow local police forces to decide which officers can carry and use Tasers, after reviewing data that suggests their use results in "fewer significant injuries" to police and the public.