The mask mandate was extended late Thursday to include the Great Southern and Wheatbelt.
The rule that masks be worn indoors is already in place in Perth, Peel and the South West.
New rules
The state government said the rule applied to anyone who has been in these regions since January 20 and comes after "new local exposure sites" were identified.
Shire of Northam president Chris Antonio said once a COVID positive case was detected in neighbouring Cunderdin, local residents anticipated masks would become compulsory.
“People were knowing it was going to be inevitable at some stage,” Mr Antonio said.
“At the Australia Day events ... there were a lot of people wearing masks because they were complying with the rules.
“So, I would say about half the people are already used to doing it or used to seeing it, so it is not a major portion of the population who have [to adjust] to adhere to the new rules,."
Posters up
In York, which also borders Cunderdin, posters were being put up on Thursday in the street and shops, advising residents and visitors of the new rules.
Shire president Denese Smythe said they could not rely on social media or emails to tell the community's many elderly residents of the new rules.
She said while she personally found masks uncomfortable, she supported the rule.
“I can tell you I do not want to put anyone else at risk and I will wear a mask because that is what is asked of me.
“I do not want anyone in York to be put at risk."
