Hundreds of patients were waiting for routine treatment at Cornwall Partnership Trust in September, figures show.
One organisation has suggested winter pressures on the NHS are already kicking in.
NHS England figures show 548 patients were waiting for non-urgent elective operations or treatment at Cornwall Partnership NHS Foundation Trust at the end of September – up from 513 in August, and 437 in September 2022.
None of those had been waiting for longer than a year.
The median waiting time from referral at an NHS Trust to treatment at Cornwall Partnership Trust was six weeks at the end of September – up from five weeks in August.
Nationally, 7.7 million people were waiting to start treatment at the end of September.
Professor Vivien Lees, from the Royal College of Surgeons of England, said: “Winter pressures have already started to affect the system.
“We are concerned that with increased demand, record staff vacancies and industrial action, this will all continue to hold back recovery efforts.”
Separate figures show 1.6 million patients in England were waiting for a key diagnostic test in September – the same as in August.
At Cornwall Partnership Trust, 151 patients were waiting for urodynamics tests.
Of them, 113 (75%) had been waiting for at least six weeks.
Recent projections by the Health Foundation suggest waiting lists will top eight million patients next year, regardless of whether industrial action continues this winter.
Strikes by health workers have been blamed by politicians for contributing to these waiting lists – but the charity's analysis suggests they are responsible for just 3% of the current waiting list.
Despite the significant challenges faced by the NHS, the Health Foundation said it was possible to clear the backlog – although it will require "sustained focus, policy action and investment".
Professor Sir Stephen Powis, NHS national medical director, said the NHS was making progress despite pressures on the service, such as industrial action.
He said: "It is important to recognise the incredible efforts of staff who are seeing and treating many more people than pre-pandemic – delivering record numbers of diagnostic tests and checks, treating more people for cancer at an earlier stage, and completing thousands more routine procedures."
He urged members of the public to get flu and coronavirus vaccinations if they are eligible.