Elizabeth Tracey Mae Wettlaufer is accused of poisoning residents who ranged in age from 75 to 90 in two Ontario facilities, the Ontario Provincial Police said at a news conference on Tuesday.
Wettlaufer, 49, appeared in Ontario Court of Justice in the city of Woodstock on Tuesday. She was charged with eight counts of first-degree murder and taken into custody.
Woodstock police received a tip on September 29 that a nurse had killed multiple patients, leading to Wettlaufer's arrest, police said in a statement.
Police would not discuss motive, citing evidence that could impact court proceedings.
Victims James Silcox, 84, Maurice Granat, 84, Gladys Millard, 87, Helen Matheson, 95, Mary Zurawinski, 96, Helen Young, 90 and Maureen Pickering, 79, were residents at Caressant Care Nursing and Retirement Home in Woodstock.
Arpad Horvath, 75, resided at Meadow Park Long Term Care in London, Ontario. He died on August 31, 2014, the last of Wettlaufer's alleged victims.
Wettlaufer's lawyers did not return CNN's request for comment.
Caressant Care Woodstock Long Term Care Home said it is cooperating with police. Wettlaufer left the home's employ two and a half years ago, spokesman Lee Griffi said in a statement.
"Our highest priority is to continue to provide for the physical, social and spiritual needs of our residents, and that remains our focus," Griffi said.
"We deeply regret the additional grief and stress this is imposing on the families involved. We are determined to avoid compromising the police investigation in any way and are therefore unable to provide any additional comment at this time."