The original campus, Old Germantown Academy and Headmasters' Houses, is listed on the National Register of Historic Places.

The Union School was founded on the evening of December 6, 1759, at the Green Tree Tavern on Germantown Avenue.

In 1777, the Battle of Germantown was fought on the front lawn of trustee Benjamin Chew at his home Cliveden less than a mile from campus.

Legend says that the British officers played the first game of cricket in America on the Academy's front lawn.

Under his leadership, the Academy gained prominence and expanded its activities with the introduction of the Inter-Academic League (1887), The Belfry Club, one of the oldest high school drama clubs in the country (1894), and The Academy Monthly (1885), one of the oldest student literary magazines still in existence.

During his headmastership, GA graduated a future University of Pennsylvania president, a Supreme Court justice, and a primate of the Episcopal Church.

Under Dr. Osbourn's leadership, the school increased in size, focused on scholarship and continued to produce some of Philadelphia's finest citizens.

Under Osbourn, GA established the eighth oldest Cum Laude Society chapter in the nation and started an endowment.

After the World Wars, GA was led by headmaster Donald Miller who was instrumental in the move from Germantown to the current Fort Washington campus.

In five years, "The Miracle of Fort Washington" (a term coined by Judge Jerome O'Neill, '28) occurred as the school moved from city to suburb.

It was first led by Barbara Hitschler Serrill,'68 and then run by longtime Head of Middle School, Richard House.

In 2011, the new Alter Middle School was constructed and opened as a part of the Building on Tradition campus campaign.

These houses include, Alcott Day, Washington, Galloway, Osbourn, Kershaw, Truesdell, and Roberts.

[5] The house system was established in 2007 at the insistence of Headmaster Jim Connor and Upper School faculty member Ted Haynie.

The seven-house system is modeled after the ancient English public school concept of joining students from different years in a common group.

Throughout the year, the houses compete in various competitions ranging from a Knowledge Bowl to a German Folk Song Singing Contest to Handball, etc.