Sir William Mulock Secondary School is a 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 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.