New South Wales has the longest land border, which is 4635 km long. it shars its border with Victoria to the south, South Australia to the west, and Queensland to the north.
The question does not make sense. All of the states of Australia share a border with another state. Even Tasmania, the island state, shares an actual land border as well as a water border with another state.
There is no Australian state which shares a border with all other states. No state except for Victoria shares a land border with Tasmania. South Australia shares a border with all mainland states and the Northern Territory.
The state of New South Wales in Australia is bordered by Queensland on the North, South Australia on the West, and Victoria to the South.
The State of South Australia completely adjoins the southern border of the Northern Territory.
South Australia borders the most states and territories in Australia. South Australia shares borders with Western Australia, the Northern Territory, Queensland, New South Wales and Victoria.
No town in South Australia lies on the border with Victoria. The closest is probably Frances, a small township with a population of about 50, between Bordertown and Naracoorte on the now disused railway line. It is about 1 kilometre west of the border.
Eucla is the easternmost town of Western Australia, near the border of South Australia.
South Australia is the only state to border both New South Wales and Queensland. in fact, South Australia is the only state to touch all mainland states as well as the Northern Territory.
The longest west-east border of South Australia is along its coastline. This part of the border, along the south, is 3816 km in length.
Poeppel Corner is where the borders of the Northern Territory, South Australia and Queenslandmeet.
South Australia's land border is 3 185 km long.