More patients were waiting for routine treatment at Lincolnshire Partnership Trust in June, figures show.
Health Secretary Sajid Javid warned that waiting lists across England will keep rising, despite the number of patients waiting for treatment reaching a new national record.
NHS Digital figures show 138 patients were waiting for elective operations or treatment at Lincolnshire Partnership NHS Foundation Trust at the end of June – up from 134 at the end of May.
However, this was 13 fewer than were waiting a year previously, when there were 151 patients on the list.
The number of people on waiting lists across England has risen to 5.45 million – the highest total for any month since records began in August 2007.
Mr Javid said he thinks waiting lists will rise even further due to the “huge increase in demand”.
He said: “The NHS has rightly focused on Covid-19 in this horrible pandemic and that has meant, sadly, that waiting lists have risen.”
Around seven million people who might have needed care during the pandemic are estimated to have stayed away and as some of them come forward to the NHS, there will be further increases in waiting lists, he said.
He added that an extra £29 billion has gone into the NHS and social care budget this year, and the Government will look at what more it needs to do.
Recent modelling from the Institute for Fiscal Studies warned the NHS waiting list could rise to 14 million by autumn next year.
NHS rules state that patients referred for non-urgent consultant-led elective care should start treatment within 18 weeks.
In signs of progress, the figures show the number of patients waiting longer than 18 weeks for care has dropped by almost 25,000.
At Lincolnshire Partnership Trust, 16 patients listed for routine treatment at the end of June had been waiting this long – 12% of all those on the list.
This was down from 35 (26%) waiting at least 18 weeks at the end of May.
There were also five patients waiting at least a year for treatment in the most recent month's data.
Professor Stephen Powis, NHS England national medical director, said the health service is experiencing one of its busiest summers ever – dealing with record patient numbers, and delivering the biggest vaccine rollout in its history.
The Health Foundation said the latest data “highlights the difficult juggling act the NHS faces in meeting emergency pressures, restoring services and addressing the backlog of care while Covid-19 cases still remain high”.
Tim Gardner, senior policy fellow at the charity, added: “The Government and NHS leaders now need to be clear and realistic with the public about how they intend to get the NHS back to full strength.
“There will need to be significant investment at the upcoming spending review if we are to see improvement on waiting lists and addressing the staff shortages which are holding back progress.”