Peel Regional Police say the stabbing happened just after 11 p.m. Thursday at a townhouse on Shipp Drive, near Hurontario Drive and Rathburn Road.
The woman, who police say is in her 50s, was taken to a local hospital with life-threatening injuries.
Const. Lilly Fitzpatrick said police have no suspect information because they've not been able to speak with the victim.
Police searched the area with a K-9 unit.
"At this point we don't know the events that resulted in her being stabbed," said Fitzpatrick. "We do have several witnesses that are being interviewed. There is nothing at this point to indicate it is domestic related, we just simply don't know the circumstances that led to this."
Fitzpatrick said other family members were home at the time of the stabbing.