Mill Hill School was founded in 1807 as a Non-Conformist Grammar School. Originally a boarding school for boys, it now offers education to boys and girls. In addition, full boarding, day and weekly boarding options are on offer. Mill Hill is the Senior School of the Mill Hill School Foundation, with Belmont, the Mill Hill Preparatory School, offering day education for pupils aged 7 to 13 and Grimsdell, the Mill Hill Pre-Preparatory School being a day school for children aged 3 to 7.

Senior Monitors
Senior Monitors would be known as Head Boy or Head Girl in other schools. Four Senior Monitors are chosen, two boys and two girls. They also share the responsibilities of the office between them. The first term of office lasts until Christmas and the second from January to July. There is also a Boarding Monitor.