Before it became the largest high school in Maryland, in terms of square footage (here’s a list of the 20 largest by enrollment), Seneca Valley High School (19401 Crystal Rock Dr. Germantown, MD) opened in its original building in 1974. The school sits on land that was once the site of a dairy farm owned by baseball player Walter Johnson. Johnson purchased the land in 1935 and lived there with his family until his death in 1946. It was Germantown’s only high school until Northwest opened in 1998.

In its first year of operation, the 1974-1975 school year, under Principal Nathan Pearson, Seneca Valley hosted students in grades seven through ten. In the following 1975-1976 school year, the school operated grades nine through eleven, with 8th graders transferring to the newly opened Ridgeview Junior High School in Gaithersburg, Maryland. During the 1976-1977 school year, Seneca Valley became a senior high school, hosting grades ten through twelve, and graduating its first class in June 1977. Finally in 1988, Seneca Valley changed to its present state of full-fledged high school with grades 9-12. The original school building was demolished in 2020 and replaced with a new building on-site in 2021.