Sir William Mulock Secondary School is an Ontario secondary school located at 705 Columbus Way, off Mulock Drive in Newmarket, Ontario, Canada. It is one of four high schools/ secondary school in Newmarket under the jurisdiction of the York Region District School Board (a fifth high school, Sacred Heart Catholic High School, is under the York Catholic District School Board) and currently educates students from Grades 9 to 12. It opened in December 2001. Prior to that, most of its students went to Newmarket High School. The founding students have demonstrated the initiative of character traits by creating original 'character feathers' which can be found in the main hall.