Thornton Academy (often abbreviated as TA) is a co-educational, independent boarding and day school serving grades 9–12 located in Saco, Maine.

The founding legislation also granted, as was common, one half a township or 18 sq mi (12,000 acres; 47 km2)[1] in northern Maine (most of what is currently the southern part of Greenville) as an endowment so long as the trustees named in the founding charter raised US$3,000 in funds.

In 1996, 54,000 square feet were added, linking the Main Building with the Scamman Science Building, and adding the Mary Hyde Library, the Helen Atkinson Dining Commons, the Harry Garland Auditorium, six arts classrooms and six math classrooms.

Because the academy has grown to nearly 80 acres (32 ha) and the buildings listed, it more resembles a university campus than a traditional American high school.

In fall 2006, Thornton Academy Middle School was opened on campus in the completely renovated footprint of the Fine Arts Building.

In the fall of 2009, Thornton Academy welcomed dozens of students from around the world in a brand new international boarding program.

In the summer of 2011, Thornton Academy built and opened a second dormitory, which is called Carl and Barbara Stasio Residence Hall, after the previous headmaster and his wife.

There is also a homestay program at Thornton Academy which enlists community host families to take in students for the school year.

Thornton Academy has a student population of 1,420, making it the largest public-private high school in the State of Maine.

in recent years has also expanded their Dorm Program to add students from various other U.S. states and foreign countries.

Fall sports include football, field hockey, soccer, cross country, volleyball, cheer leading and golf.

Winter sports include basketball, cheerleading, indoor track, ice hockey and swimming.

On November 17, 2012, the Thornton Academy football team beat Lawrence at Fitzpatrick Stadium to become the 2012 Maine State Class A Champions.

On November 22, 2014, the Thornton Academy football team beat Windham at Fitzpatrick Stadium to become the 2014 Maine State Class A Champions.