The township was created in 1819, its name derived from the Mississauga word nazhesahgewayyong, meaning 'river with two outlets.'
This refers to the fact that watercourses in the township drain to both Lake Ontario and the Grand River system.
Communities within the boundaries of the former township include: Campbellville, Brookville, Moffat, Haltonville, Darbyville, Guelph Junction and Sayers Mills.
Nassagaweya historically contained Eden Mills and borders on Kilbride.
This Ontario geographical article about a location in the Golden Horseshoe is a stub.