Simcoe South was a federal electoral district represented in the House of Commons of Canada from 1867 to 1925, and from 1979 to 1988.

The South Riding consisted of the Townships of West Gwillimbury, Tecumseh, Innisfil, Essa, Tossorontio, Mulmur, and the Village of Bradford.

The South Riding consisted of the townships of Mulmur, Tossorontio, Essa, Innisfil, and Tecumseth, and the village of Alliston.

In 1903, the south riding was redefined to consist of the townships of Adjala, Essa, Gwillimbury West, Innisfil, Tecumseth and Tossorontio, the towns of Alliston and Barrie, and the villages of Beeton, Bradford and Tottenham.

It consisted of the City of Barrie and the Townships of Essa, Flos, Innisfil, Tecumseth, Vespra and West Gwillimbury, but excluding the Towns of Alliston and Wasaga Beach.