The school is named after Sir William Mulock, an important figure in Canadian politics at the end of the 19th century, leading into the 20th century. He was one of the most prominent residents of Armitage, the first community established in King that has since been subsumed by Newmarket. The founding principal of SWMSS was Reet Patterson. Carmen Spiteri-Johnson is the current principal, and approximately 1200 students attended the school during the 2010/11 school year. Sir William Mulock Secondary School offers a variety of programs in: Business, Laboratory Experiments, Earth & Space Sciences, Computer Studies, Engineering, Woodworking, Co-operative Education, Lifestyles, Fashion, English, Family Studies, Geography, Law & Politics, History, Library Studies, Biology/Medical Studies, Mathematics, Modern languages - French, Spanish, Latin, Portuguese, Chinese and Italian; Health, Music, Orchestral Studies, Dance, Physical Education, Science, Special Education, Technical Studies, Drama and Visual Arts. Mulock also offers many sports teams and clubs for students. The school is also limited in courses compared to other secondary schools in the area; this can be attributed to the relatively short establishment period. The first graduating class was in 2004.
Feeder schools
The main feeder schools for Sir William Mulock Secondary School are:
Starting the 2010/2011 year, the Grade 9 students of the school participated in a new program. Students are now required to bring netbooks/laptops with wireless capabilities to classes throughout the year. After a successful first year for the program, it was implemented in grades 10, 11, and 12. This model is now being implemented at several other York Region District School Board schools. This program was introduced to modernize teaching and learning methods by blending traditional and technological teaching strategies.
Dress code
This is a public school therefore, the use of uniforms is not required. There is however, a dress code policy. Such inappropriate clothing includes short shorts, gang colours, and headbands over an inch thick. As of September 8th 2015, hats are allowed to be worn indoors.
School mascot
Sir William Mulock Secondary School's mascot is Billy the Raven.