Ten out of 26 beds for mental health patients in an adult psychiatric unit were being used unnecessarily, it has emerged.
The figures came after patients were assessed following a fire alert at Longreach House in Redruth in 2014.
Cornwall Partnership Trust blamed the "prolonged time" taken by the NHS to decide on funding of patients' care.
The government hopes to eliminate inappropriate out-of-area placements for adults in acute care by 2021.
More on the bed blocking story, plus other Devon and Cornwall news
Twenty-six patients were receiving acute care at Longreach House, said a report into the fire alert for the Journal of the Royal Society of Medicine.
The fire alert led to the patients' ward being closed for six months.
'Distressing for families'
But when the patients were assessed for alternative accommodation, only 10 were deemed to need an acute bed, said the report.
Report author Dr Richard Laugharne, of the Cornwall Partnership Trust, said the "prolonged time taken for funding assessments" led to "inappropriately long stays in acute psychiatric wards for some patients with chronic needs".
He said that so-called bed-blocking resulted in new admissions of acutely unwell patients having to go to out-of-county hospitals.
"This is distressing for them and their families and friends," he said.
In July Cornwall's coroner raised concerns with the health secretary over the care of mentally ill patients far from home.
It came after an inquest jury concluded the death of a man from St Austell was suicide, while undergoing care 140 miles from where he lived.