Mount Pleasant Academy, opened in 1814, was a major educational institution for more than a century, offering a range of subjects to students of both genders until it was transformed into a military school in 1848, after which its student body consisted only of male cadets studying a curriculum modeled after that of the West Point Academy. Its library building, erected in a decorative Late Victorian style in 1878, is the academy’s only surviving building, and at that time the academy library contained more than 12,000 books. The Mount Pleasant Military Academy closed in 1925, after which the building became the offices of surveyor William Arthur Slater, whose collection of more than 4,000 glass plate photographic negatives is now at the Ossining Historical Society.