Royal Cornwall Hospitals NHS Trust was caring for 19 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 September 17 was up from 16 on the same day the previous week.
Across England there were 3,019 people in hospital with Covid as of September 17.
Nationally, the number of hospital patients with Covid-19 has increased by 18% in the last four weeks.
The figures also show that 22 new patients with Covid were admitted to hospital in Royal Cornwall Hospitals NHS Trust in the week to September 15.