Terang, Noorat, Mortlake, Caramut and Peterborough residents will be voting for different MPs in state elections under proposed boundary changes.
Lowan, held by Nationals' Emma Kealy and based around Horsham, would spread further south.
South West Coast, held by Liberal Roma Britnell, will spread east and Polwarth, held by Liberal Richard Riordan, will be reduced in size.
The state electoral boundary redivision report released on Wednesday proposed voters in Caramut would be transferred from South West Coast to Lowan.
Mortlake would also move to Lowan from Polwarth while Terang, Noorat and Peterborough would be transferred to South West Coast.
Portland, which had previously been earmarked for change, will remain in South West Coast.
Eight submitters, including the Australian Labor Party, Liberal Party and One Nation, favoured Lowan expanding south to the coast, to include Portland.
But the Electoral Boundary Commission decided against it, stating that although Portland was in Glenelg Shire, "it is in some ways quite distinct from the northern part of the shire that is currently in Lowan district".
"The northern area around Casterton is rural with an economy based largely on sheep raising, and has closer links with Hamilton (64 kilometres away) than with Portland (103 kilometres)," the report said.
"In contrast, Portland is an industrial and maritime town. It has arguably closer links with Warrnambool, along the coast, than with the inland areas to the north.
"Under the suggested option, Lowan District would need to shrink, shedding towns such as Warracknabeal and Murtoa, which have strong associations with Horsham, and splitting the Wimmera community that is a strong part of Lowan district's identity."
The EBC favoured the second option, to expand Lowan district to the east, as suggested by 12 submitters, including The Nationals and the Australian Greens.
In the east, the EBC proposed to transfer 5585 electors in Stawell, Great Western and Glenorchy from Ripon to Lowan, using the Wimmera River as a boundary.
In the south-east, the EBC proposed to transfer 1591 electors in the Mortlake area from Polwarth to Lowan.
That area has a link with Hamilton along the Hamilton Highway, and a clear eastern boundary following the Moyne Shire boundary and Mount Emu Creek.
The district boundary would be strengthened by transferring 114 electors in Caramut from South West Coast to Lowan.
Lowan's enrolment would be 4.68 per cent above the average, and will remain comfortably within the 10 per cent tolerance over the forecast period.
The loss of Mortlake goes only part of the way to reducing Polwarth District to within the 10 per cent margin.
A further adjustment was to expand South West Coast to the east.
The EBC proposed to shift the boundary east to the Moyne Shire boundary and to include Terang and Noorat, with a boundary following Mount Emu Creek.
"The eastern fringe of Moyne Shire has close associations with Warrnambool and, although Terang is in another Shire, it is closer to Warrnambool (45 kilometres) than it is to Colac (73 kilometres), the main centre of Polwarth District," the report said.
The addition of 3285 electors puts South West Coast's enrolment at 6.69 per cent above the average, and likely to remain stable.
South West Coast MP Roma Britnell said she was pleased the electorate remained largely unchanged and retained Portland, Heywood and the lower section of the Glenelg Shire.
She said the proposed changes to the eastern boundary of South West Coast would add Terang, Noorat and Glenormiston and Peterborough to the electorate and making small changes on the north eastern boundary.
"I look forward to meeting the new constituents that will be joining the South West Coast electorate." she said.
"The Electoral Boundaries Commission is now calling for feedback on the draft boundaries and I would encourage anyone with thoughts on the redistribution and the proposed new boundaries to make a submission."
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