| Province: | Ontario |
| Fed-Status: | defunct |
| Fed-Created: | 1867 |
| Fed-Abolished: | 1933 |
| Fed-Election-First: | 1867 |
| Fed-Election-Last: | 1930 |
Perth South was a federal electoral district represented in the House of Commons of Canada from 1867 to 1935. It was located in the province of Ontario. It was created by the British North America Act of 1867, which divided the County of Perth into two ridings. The South Riding of the County of Perth initially consisted of the Townships of Blanchard, Downie, South Easthope, Fullarton, Hibbert, and the Villages of Mitchell and St. Marys.
In 1882, the townships of Usborne were added to the riding, and that of South Easthope was excluded. In 1903, Usborne was removed from the riding, and Easthope South and Logan townships were added. In 1914, the part of the village of Tavistock situated in the township of Easthope South was added.
In 1924, Perth South was defined to consist of the part of the county of Perth lying south of and including the townships of Logan, Fullerton and Downie, south of but excluding the city of Stratford, south of but including the township of Easthope South to the east boundary of the said county. That part of Tavistock lying in the township of Easthope South was also included.
The electoral district was abolished in 1933 when it was redistributed between Huron—Perth and Perth ridings.
This riding has elected the following members of Parliament:
|- |Liberal|Robert MacFarlane|align="right"|1,490 |Unknown|T. B. Guest|align="right"|1,393 |- |Liberal|James Trow|align="right"|1,683 |Unknown|J. Kidd|align="right"| 1,256 |}|- |Liberal|James Trow|align="right"| acclaimed |}|- |Liberal|James Trow|align="right"| 1,796 |Unknown|E. Hornibrook|align="right"|1,719 |}|- |Liberal|James Trow|align="right"| 1,896 |Unknown|Thomas B. Guest|align="right"| 1,717 |}|- |Liberal|James Trow|align="right"| 2,224 |Conservative|H. F. Sharp|align="right"|2,131 |}|- |Liberal|James Trow|align="right"| 2,363 |Conservative|H. F. Sharp|align="right"| 2,186 |}|- |Conservative|William Pridham|align="right"|acclaimed |}|- |Liberal|D. K. Erb|align="right"| 2,069 |Conservative|William Pridham|align="right"| 1,851 |Protestant Protective|J. A. Donald|align="right"|551 |}|- |Liberal|Dilman Kinsey Erb|align="right"| 2,169 |Conservative|William Pridham|align="right"| 2,160 |}|- |Liberal|Gilbert H. McIntyre|align="right"|2,454 |Conservative|Michael Steele|align="right"|2,310 |}|- |Liberal|Gilbert Howard McIntyre|align="right"|2,412 |Conservative|Michael Steele|align="right"| 2,383 |}|- |Conservative|Michael Steele|align="right"| 2,303 |Liberal|Gilbert Howard McIntyre|align="right"| 2,221 |}|- |Government|Michael Steele|align="right"| 2,770 |Opposition|William Forrester|align="right"| 2,713 |}|- |Liberal|William Forrester|align="right"| 3,209 |Conservative|Michael Steele|align="right"| 2,948 |}|- |Liberal|Frederick George Sanderson|align="right"| 4,455 |Conservative|Robert S. Graham|align="right"| 4,041 |}|- |Liberal|Fred George Sanderson|align="right"| 4,966 |Conservative|Robert S. Graham|align="right"|4,451 |}|- |Liberal|Frederick George Sanderson|align="right"| 5,063 |Conservative|Samuel James Monteith|align="right"| 4,346 |}