The following paragraph is based on an article in Wikipedia.
Dummer Township was opened for settlement in 1821 and named in honor of William Dummer Powell, Chief Justice of Upper Canada. A "colony" of immigrants arrived in 1831, of whom 150 were sent out by the Marquess of Bath.
Ontario GenWeb has a sketchmap of the original townships.
The map of Peterborough County circa 1951 from Ontario Archives locates the individual municipalities, townships, city, towns and villages of the county.