Cornwall Partnership Trust was caring for four patients with coronavirus in hospital as of Sunday, figures show.
NHS England data shows the number of people being treated in hospital with Covid-19 by 8am on March 17 was up from one on the same day the previous week.
Across England there were 1,690 people in hospital with Covid as of March 17.
Nationally, the number of hospital patients with Covid-19 has decreased by 34% in the last four weeks.
The figures also show that four new patients with Covid were admitted to hospital in Cornwall Partnership NHS Foundation Trust in the week to March 15.