Information obtained by The Echo through a Freedom of Information (FoI) request revealed the average waiting time for patients in the emergency department at the Mercy was 8.6 hours before they were admitted, discharged, or treated.
The HSE has said that patients should wait no more than six hours.
The Echo sought the information on waiting times amid continuing overcrowding concerns at Cork hospitals, and was given the average waiting figures for the entire month of February.
The figures for the Mercy were revealed after a chaotic period in Cork University Hospital last week when patients were waiting for more than 12 hours during a status black escalation, deeming it clinically unsafe to admit more patients.
A spokesperson for the Mercy told The Echo that more and more elderly people were presenting at the A&E, which was having a knock-on effect on the waiting times.