Milliken Mills High School is a high school in the city of Markham, Ontario, Canada. It is one of 33 high schools in the York Region District School Board. The high school's construction was not scheduled to finish until January 1989 because of a construction worker strike. The students were sent to Unionville High School on September 1988 for the first semester of the school year. Unionville High students went to school from 8:00 am to 12:00 pm and the Milliken Mills students went to school from 1:00 pm to 4:30 pm. Milliken Mills was fully operational in Spring, 1989.