St. Pierre, 65, was pronounced dead just after 9:20 a.m. Saturday after paramedics responded to his home in Russell, Ont., south of Ottawa.
The cause of death has not been released. St. Pierre was reportedly in good shape and didn't have any prior health problems.
His death comes a mere nine days before municipal elections take place across Ontario. St. Pierre was running for mayor against his cousin Donald St. Pierre.
St. Pierre spent about 30 years involved in politics in rural eastern Ontario. He was also the Warden of the United Counties of Prescott-Russell and this year he was named the 2014 chairman of the Eastern Ontario Wardens’ Caucus.
He began to head the wardens’ caucus, an organization that lobbies politicians at Queen’s Park, last January. The caucus speaks for 11 counties in eastern Ontario and two single-tier municipalities, representing about 750,000 residents.
In that role, St. Pierre had recently vowed to pressure the province to reduce costs for municipalities who use Ontario Provincial Police.
St. Pierre, a retired RCMP officer, was interviewed just last week by Radio-Canada as he spoke about his priorities if re-elected.
Councillors and staff met on Saturday as they try to determine their options moving forward. There is only one candidate left on the ballot, St. Pierre's cousin, but staff said they would reach out to Elections Ontario to ask about their options.