Donnybrook-Balingup, Boyup Brook, Bridgetown-Greenbushes and Manjimup can expect to see the National Disability Insurance Scheme (NDIS) rolled out from July next year.
Eligible people in WA will get access at different times over the three-year transition period from July 2017 to July 2020, depending on the region they live in.
It comes after the state and federal governments finalised negotiations on a nationally-consistent, WA-delivered NDIS, signing a bilateral agreement on Wednesday.
"This agreement confirms that West Australians with severe and permanent disability will have access to the reasonable and necessary supports they need and now sees all of the Australian population covered by full bi-lateral agreements," Commonwealth Social Services Minister Christian Porter said.
"There were 11 fixed conditions the Commonwealth required for a state-run NDIS in Western Australia to ensure consistency and integrity of the scheme is upheld across the country and I'm very pleased the agreement reflects all of these conditions.
The scheme will be delivered by a new WA NDIS authority and will be governed by a seven-member independent WA Board.
WA Disability Services Minister Donna Faragher said about 39,000 people would be part of the WA NDIS by the end of the transition phase.
"Western Australia has a long tradition of significant investment in disability services - this Government strongly believes people with disability deserve quality services no matter where they live,” she said.
"We are prepared to invest what it takes to ensure that the NDIS can be rolled out to every eligible person in WA no matter where they live. Importantly, this agreement provides the opportunity for West Australians with disability to continue to shape how the scheme can best meet their needs into the future."
People already receiving services through NDIS trial models in WA will see minimal disruption as a result of announcement, she said.
As part of the agreement, the Commonwealth will fund about 40 per cent of average package costs for people aged up to 64 and WA will cover the remaining 60 per cent.
All the operational costs of the WA NDIS authority will be met by WA.
