Peterborough (pronounced Pee-ter-bor-row) is a city on the Otonabee River in (Central-Eastern) Southern Ontario, Canada, 125 kilometres (78 miles) northeast of Toronto. The population of the City of Peterborough was 74,898 in the 2006 census, while the census metropolitan area (CMA) had a population of 116,570. It presently ranks as the 33rd and smallest CMA in Canada.The current mayor of Peterborough is Daryl Bennett.

Peterborough is known as the gateway to Kawarthas, “cottage country”, a large recreational region of the province. It is named in honour of Peter Robinson, an early Canadian politician who oversaw the first major immigration to the area.

Peterborough is situated in South Eastern Ontario, on the northeastern edge of the Greater Golden Horseshoe and heart of the Kawartha Lakes region in Ontario. Peterborough lies in the St. Lawrence Lowlands ecoregion in Canada, just south of the Canadian Shield and about 35 kilometres north of Lake Ontario. The city is centred around a series of rapids in the Otonabee River, approximately halfway between where it begins at Katchewanooka Lake and where it empties into Rice Lake. The urban area of Peterborough completely surrounds the only lake on the Otonabee, Little Lake, and the Trent Canal runs along the eastern edge of the city, connecting Little Lake to a section of the Otonabee above the rapids.