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 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 its doors in December 2001. Prior to that, most of its students went to Newmarket High School.