Some vacation agencies illegally offer accommodation during the coronavirus outbreak, counsel said.
The Cornwall Council said it had received complaints that some providers were still hosting guests, despite the lockout.
Malcolm Bell, general manager of Visit Cornwall, said the Airbnb website still advertises the holidays.
Airbnb said it reminded hosts to review government advice “before accepting reservations.”
The Cornwall Council said it wrote to all vacation home owners and rental platforms in the county because “a small minority” of businesses continued to operate.
Boris Johnson has announced that most hotels and similar businesses in the UK are to close during the closure period.
The board said companies could face “coercive measures” if they did not obey orders.
He said there were exemptions allowing businesses to remain open during this period, for example to provide accommodation for key workers, NHS staff and health and care.
Mr. Bell said, “The truth is that there is no reason to be open for business, in fact, it is illegal to be open for business.
“I am furious because these are big powerful companies and it must be the same in the world, it is not difficult to know that there is a lock in Great Britain, in England, in Cornwall, it just tell your computer programmers that there is no availability. “
An Airbnb spokesperson said, “On Sunday we announced a platform where Airbnb hosts provide free accommodation to the NHS and other front-line medical staff and Airbnb will waive all fees associated with stays.
“We are in regular discussions with the government about travel restrictions during the closed time and have introduced measures and advice for hosts and guests. “