Thornton is an unincorporated place in Essa Township, Simcoe County, Ontario, Canada. It had a population of 986 as of the 2016 Census. It is 74 kilometres north of Toronto. The town of Thornton developed during the 1820s, and in 1833 was established as Henrysville after early settler John Henry, who was the first teacher and then the schoolmaster, and lateā¦Thornton is an unincorporated place in Essa Township, Simcoe County, Ontario, Canada. It had a population of 986 as of the 2016 Census. It is 74 kilometres north of Toronto. The town of Thornton developed during the 1820s, and in 1833 was established as Henrysville after early settler John Henry, who was the first teacher and then the schoolmaster, and later became the postmaster when an office opened in 1854. The name Henrysville caused confusion in the mail system at the time, so the community became Thornton in 1854 after Henry Thornton, who owned a grist mill, saw mill and planning mill.