South Australia has just one active case of coronavirus as the state's run without new infections stretches to five days.
The latest SA Health data shows the state last reported a positive test on August 23, when a nurse who worked to help stem Victoria's COVID-19 second wave returned to Adelaide.
Earlier this year, South Australia went more than a month without new cases and has only reported 35 since April 11.
The state's total since the start of the pandemic remains on 463 with more than 360,000 tests taken over that period.
The latest clean sheet came as more coronavirus measures were relaxed with communities near the Victorian border given back their freedom to move between the two states.
From Friday, people living or working 40 kilometres each side of the border are allowed to come and go but will be subject to regular COVID-19 testing.
The buffer zone was dropped last week, closing SA off to everyone except essential travellers coming from Victoria.
Premier Steven Marshall said the easing of restrictions was possible because the remaining virus cases in regional areas, close to South Australia, had been cleared.
"We've always said we wanted to remove that restriction the very second that we could," Mr Marshall said.
"It has been an enormous imposition on those border communities. We apologise for the inconvenience and frustration."
In other changes now in place, people travelling to SA from Queensland, the Northern Territory, Western Australia and Tasmania who transit through the Sydney or Canberra airports will no longer need to self-isolate for two weeks.
Home gatherings in SA can also increase from 20 people to 50.