Its main building was built in 1883 by Major Edward S. Sanborn (died 1885) to serve as a secular secondary boarding school.

The campus became known as Sanborn Regional High School and served students from the towns of Kingston, Newton, and Fremont.

The facade bays are otherwise articulated by brick pilasters, and have pairs of narrow windows, each with stone keystones, shoulders, and sills.

The Seminary is the centerpiece of a campus complex that originally included five additional wood-frame structures and a beach recreation area on nearby Greenwood Pond.

The bell tower was removed from the building's roof and located on the East Lawn until 2006, when it was relocated to the new Sanborn Regional High School atrium.