Adjala–Tosorontio is a township in south-central Ontario, Canada, in the County of Simcoe .
A predominantly rural area, Adjala–Tosorontio contains numerous small villages and hamlets. Many communities were started in Adjala by Irish Catholics who named their hamlets after their home towns in Ireland, or after prominent pioneer families who first settled the area. The municipality has increasingly become home to residents who commute to the Greater Toronto Area.
Geographically the area is rolling countryside below the Niagara Escarpment to the west, with the Nottawasaga-river cutting through it.
“Tosorontio” is a Huron word meaning “Beautiful Mountain”, and Adjala was the name of the wife of Chief Tecumseh, for whom the neighbouring township (now called New Tecumseh) was named.