Four stores and eight apartments were damage early Tuesday when fire ripped through the two-storey building erected in 1867.
The blaze broke out in a photo shop and fire officials believe it started in either the basement or the main floor of the building.
There were no injuries.
Local firefighters were helped by colleagues from Oshawa and Ontario Power Generation's Darlington nuclear facility.
Mayor Jim Abernathy says the Maplefest street festival on Saturday _ a major local event that draws about 20,000 people _ will go on.