Petersburg is an unincorporated community in Wilmot Township in the Regional Municipality of Waterloo, Ontario, Canada. It is recognized as a designated place by Statistics Canada.

The village was settled and named afer Peter Wilker, a native of Hesse-Darmstadt, Germany in the 1830's.

The locality had a school in 1842, a post office in 1849 amd in 1856, the locality was a station on the Grand Trunk Railway.

In the 2021 Census of Population conducted by Statistics Canada, Petersburg had a population of 374 living in 147 of its 149 total private dwellings, a change of 10% from its 2016 population of 340. With a land area of 0.66 km (0.25 sq mi), it had a population density of 566.7/km (1,467.7/sq mi) in 2021.

• Harold Albrecht, member of the House of Commons of Canada from 2006 – 2019.
• Glen Cressman, ice hockey player.
• Albert Heer, mayor of Waterloo, Ontario from 1944 to 1946.

• List of communities in Ontario
• List of designated places in Ontario