[4] The first Allen High School, built in 1910 at the corner of Belmont and Cedar, was a two-story brick building housing six classrooms and an auditorium, and saw the first graduating class of eight students in 1914.

The second Allen High School was established in 1959 at the corner of Jupiter and Main Streets on land donated by Mr. Harris Brown.

[5][6] In August 1999, Allen High School "2000," a new facility at the corner of Greenville and Rivercrest, opened to 2,200 students in grades 10 through 12.

The southernmost part of the school was renovated into the Dillard Special Achievement Center, while the northern section became a parking lot.

This expansion included a new 1,500 seat performing arts center, an expansion of band hall space and a Career and Technology Education center featuring a student-managed restaurant open to the public, a student-managed apparel store with student-designed items, multiple new Mac labs, Mac-equipped rooms for the photojournalism, yearbook, commercial photography, audiovisual, radio, and newspaper classes as well as learning-classrooms for the medical education programs.

Allen High School offers the International Baccalaureate program to its students, with the class of 2002 being the first to graduate Full Diploma.

[10] Allen High School features a Career and Technical Education (CTE) campus known as the STEAM Center, which opened in 2019 at a cost of $40 million.

[12] The STEAM Center can accommodate over 500 students simultaneously and includes a range of advanced amenities, such as an OmniGlobe, a large maker space, and a lake.

[64] Due to the program's popularity and student population, the school was authorized, via an approved April 2009 referendum, to build an 18,000-seat stadium for the team.