NHS England statistics show 33,586 patients were waiting for non-urgent consultant-led care at Mid Yorkshire Hospitals NHS Trust which runs Pinderfields, Pontefract and Dewsbury hospitals, at the end of April.
This is 254 more than 33,332 the month before.
Castleford care home Fairburn Mews ordered to improve after inspectors found residents 'at risk of harm'
Wakefield woman diagnosed with brain tumour takes on charity walking challenge
Number of Covid patients being cared for by Mid Yorkshire Hosptials
18 of the worst Wakefield neighbourhoods for Covid vaccinations as BA4 and BA5 cases surge
Wakefield MP Simon Lightwood warns of ‘healthcare black hole’ as health bosses consider closing King Street NHS walk-in centre
The figure was also a 12% increase on the 29,954 on the waiting list in April last year.
Across England, the number of people waiting for treatment rose by 171,720 from almost 5 million in March to 5.1 million in April – the highest number since records began in August 2007.
The Health Foundation said the backlog offered a "stark reminder" of the task ahead for the NHS, adding greater investment as well as support for innovative ideas was needed.
Tim Gardner, senior policy fellow, said: "Making incremental improvements to business as usual, while important, will not be enough to address a challenge of this scale."
Meanwhile, The King’s Fund said the Government needed to be honest with patients about the time it would take to bring waiting lists under control.
Deborah Ward, senior analyst at the think tank, said: “For those with more severe conditions, long waits could mean months spent in increasing pain or facing the prospect that treatment will be less effective."
NHS rules state that patients referred for non-urgent consultant-led elective care should start treatment within 18 weeks.
But the figures show 1,501 had been waiting more than a year for treatment at Mid Yorkshire Hospitals NHS Trust in April – down from 1,765 in March but higher than the 13 who had been waiting this long in April last year.
There were even one patient on the list who had been waiting for more than two years at the end of April.
Across England, the number of patients waiting more than a year fell to 385,490 in April, from 436,127 in March.
However, this was still a vast increase on the 11,042 in April 2020.
NHS England said the data showed operations and other routine care were "ahead of ambitions" set out in April.
The organisation announced last month it was investing £160 million on an initiative to find new ways of tackling the vast backlog of care.
Professor Stephen Powis, national medical director for NHS England, said: "Despite the extensive disruption to care caused by the pandemic, it’s encouraging that today’s figures show routine operations, cancer and mental health care have now all rebounded sharply."