Hundreds of patients were waiting for routine treatment at Cornwall Partnership Trust in July, figures show.
The shadow health secretary has branded the Prime Minister "inaction man" over rising waiting lists.
NHS England figures show 405 patients were waiting for non-urgent elective operations or treatment at Cornwall Partnership NHS Foundation Trust at the end of July – up from 313 in June, but a decrease on 560 in July 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 four weeks at the end of July – down from six weeks in June.
Nationally, 7.7 million people were waiting to start treatment at the end of July.
Shadow health secretary Wes Streeting said patients were waiting an "unacceptably long" time.
He added: "On the NHS, Rishi Sunak is Inaction Man, refusing to meet with doctors to end NHS strikes and adding to the Conservatives’ NHS backlog, leaving patients waiting for months on end in pain and agony."
Separate figures show 1.6 million patients in England were waiting for a key diagnostic test in July – the same as in June.
At Cornwall Partnership Trust, 143 patients were waiting for urodynamics tests.
Of them, 95 (66%) had been waiting for at least six weeks.
Professor Pat Price, of the CatchUpWithCancer campaign, said the cancer figures show "we are still massively short in hitting the Government’s target of no more than 85% of cancer patients waiting more than 62 days between urgent GP referral and their first treatment."
"Today’s figures reveal that nearly 40% of cancer patients are missing their life-saving cancer treatment: this is over double the Government’s own target," she added.
The Prime Minister told the BBC on Thursday ongoing strikes by NHS staff were threatening his target of cutting waiting lists in 2023, acknowledging his promise could be missed.
Professor Julian Redhead, NHS England’s national clinical director for urgent and emergency care echoed Mr Sunak's comments on the impact of industrial action.
He said: “Today’s figures show that despite ongoing pressures across the NHS, including record demand for emergency care this summer, and an increase in Covid cases during July and August, NHS staff are continuing to deliver for patients."