A correctional officer at the Hamilton-Wentworth Detention Centre was sent to hospital by ambulance after falling ill on shift early Thursday afternoon.
And several other correctional officers from the same shift also went to hospital as a precaution, the Ministry of Community Safety and Correctional Services told CBC Hamilton.
The ministry said it is investigating the situation.
It provided no information about the nature of the illness.
"It would be inappropriate for the ministry to publicly comment further out of respect for personal health information." said Andrew Morrison, ministry spokesman.
Police had earlier confirmed that there was an ongoing situation at the Hamilton Wentworth Detention Centre.
According to Hamilton paramedic supervisor, Linda Minas-Connolly, one male in his 30's in medical distress has been transported to hospital.