Almost 100,000 sick notes were given to patients in Kernow last year, new figures show.
The figures come as a health charity warns long-term ill health is having profound consequences on workers, employers, and the Government's finances.
Since 2012, GPs have been able to give patients electronic 'fit notes', which say whether the patient is too sick to return to work, or give other recommendations, such as a phased return to work.
NHS Digital data shows 94,285 of these notes were given to patients in the former NHS Kernow CCG area in the year to June – equivalent to 28,028 for every 100,000 registered patients.
Across England, the number of fit notes rose to 10.4 million in the year to June, up 8.6% from 9.5 million in the year to June 2019.
There has also been a significant national increase in fit notes given for long durations – 132,000 fit notes were issued for leave of 20 weeks or longer in the year to June, up 42% from 93,000 three years prior.
It has been suggested that 'long Covid' – a range of coronavirus-related symptoms which remain after the initial period of infection has passed – could be contributing to the increase in workers being signed off for longer periods, alongside lengthy waiting lists for NHS treatment since the start of the pandemic.
The Health Foundation, a charity which carries out research on healthcare, said that this rise in sickness duration was "incredibly worrying" and could have disastrous consequences if people are forced to leave work altogether.
In the year to June, 4.3 million notes – or 42% of all fit notes – were for leave of a month or longer, up from 3.3 million – 34% – in 2018-19.
Dave Finch, assistant director at the charity, said that long-term sickness is especially tough on those trying to make ends meet during the cost-of-living crisis.
"It will be bad news for employers, especially in areas with severe skills shortages – and it will add costs for the state too, when pressures are going up and money available is going down," he added.
Data from the Office for National Statistics shows the number of people off work due to long-term sickness in the UK is at all-time high, with 2.49 million people now 'economically inactive' due to ill health.
In response, Mr Finch said businesses need to be open to mitigating circumstances for their employees, and that the Government should consider greater financial support for workers while they are off sick.
A spokesperson for the Department of Health and Social Care said they have published updated guidance to employers on how to support employees that are managing a health condition.
They added: “For anyone with a disability or long-term health condition, including long Covid, there is a strong financial safety net, including Statutory Sick Pay, Employment and Support Allowance and Universal Credit."
In July, clinical commissioning groups were abolished and replaced with integrated care boards across England.