Environment Canada confirms a tornado touched down in the community of Grand Bend on the southeastern shore of Lake Huron.
The weather service says an EF1 twister with winds between 155 and 175 km/h hit the area Sunday night.
Meanwhile, more than 4,000 Hydro One customers in the Grand Bend area remained without power Monday after the storm ripped through southwestern Ontario.
Hydro One spokeswoman Dana Gardner says crews were working to restore power and that all homes and businesses were expected to be back online by 11 p.m.
On Monday afternoon an investigation by Environment Canada confirmed the twister in the Grand Band area -- about 70 kilometres northwest of London -- where utility poles and trees were knocked down during the storm.
Provincial police say one injury was reported during the storm, but they could not immediately confirm whether it was storm-related.
Other parts of Ontario also faced adverse weather during the night, with severe thunderstorms stretching all the way from Windsor to Kingston. Many smaller-scale outages were reported, Hydro One said.
The municipality of Lambton Shores, which covers Grand Bend, issued a news release saying strong winds have caused "significant damage" and urging people to stay clear of downed power lines.
"Public works and hydro crews worked through the night," it read, adding that work was continuing Monday.
