St. Mary Catholic Secondary School, Cobourg

St. Mary Secondary School is a high school in the city of Cobourg, Ontario. It provides classes for 800 to 900 students as of October 2015. St. Mary CSS campus is located on the wooded property along Birchwood Trail in Cobourg, about 95 km east of Toronto, in Central Ontario, Canada. The school has been part of the Cobourg community for over 20 years.

The school was founded in 1984 and has been located at its current site since September 1998 with a new wing of 12 classrooms added in 2005.

Sports teams at St. Mary have won OFSAA titles in rowing, badminton, swimming, rugby, and javelin.