West Hertfordshire Hospitals NHS Trust, which runs Watford General Hospital, missed its A&E waiting target of seeing patients in less than four hours last month.
Hospitals are meant to treat, assess or discharge 95% of patients in that time. West Hertfordshire Hospitals Trust saw 81.2% according to figures released for April. This is down on the figure for 12 months ago, which was 87.6%.
At West Hertfordshire Hospitals NHS Trust a total of 2,464 patients were not seen within the four-hour window in April.
The trust was ranked 76 of 129 trusts of hospital trusts in England.
As a whole, the NHS has failed to meet this target since July 2015. A hospital trust's performance figures include the main accident and emergency department and any minor injuries or care centres it runs.
NHS England has asked patients only to attend A&E department with "genuine life-threatening emergencies".
This story has been generated using NHS data, BBC analysis and some automation.