Dana Gardner, a Hydro One spokeswoman, said crews were working to restore power, and that all homes and businesses were expected to be back online by 11 p.m.
Environment Canada has yet to confirm reports of a tornado in the Grand Band area — about 70 kilometres northwest of London — where utility poles and trees were knocked down during Sunday night's storm.
Provincial police said one injury was reported during the storm, but they could not immediately confirm whether it was storm-related.
Geoff Coulson, a meteorologist at the weather agency, said it's possible either a tornado or a "burst of damaging winds" hit the area.
The weather agency is sending a team to the area to investigate, Coulson said.
"Bursts of damaging winds can have wind speeds that rival those found in many of the tornadoes in Ontario, but it tends to be a big gust of wind that comes out of the front end of the storm," he said.
"It tends to be broader in its path, pushing everything over in generally one direction."
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.