Armitage Academy was founded in 1975, but its originating roots trace back to 1855, with the establishment of "Kemper Hall", a Kenosha Female Seminary. In 1865, Kemper Hall, (named after Jackson Kemper, the Anglican missionary priest who later became Bishop of Wisconsin), fell into some hard times and almost closed its doors. After the death of Bishop Jackson Kemper, the new Bishop William Armitage, of Milwaukee, implemented a restructuring of the Seminary. Kemper Hall was converted, under the directorship of the Sisters of St. Mary, into a private girls' boarding school. It remained in existence until 1975, when once again Kemper Hall fell into financial difficulties and ultimately had to close its doors.

Upon hearing of the closing of Kemper Hall parents, teachers, alumni and community members banded together and discussed opening a private coed elementary day school. Symbolically, it was felt seeing that Bishop Armitage saved the school once and the school was once again being saved, the rebirth of the new private independent school in Kenosha was to be known as Kenosha Day School doing business as "Armitage Academy". In 1975,the new non-sectarian school opened its doors in four rented rooms in a church on 75th street. Within 3 years of its opening the growth of Armitage became over whelming and the school purchased a historic building in the downtown Library Square area. Today this is the main entrance to the school and now houses the main office, auditorium, lunch room, fine art classes and administrative offices.

The continued growth of the school was stymied by over crowding conditions. Classes began spilling into hallways and seeing the need, prompted a move of grades 4, 5, and 6 two blocks down the street to the Kenosha Youth Foundation. Additional space was finally added when a new semi-open classroom building was built adjacent to the current building in 1994. This added 17,400 square feet of space is now the home for all classes Kindergarten through 8th grade. The new design of the school moved Armitage toward a more experiential learning approach. The open class room environment allowed students to become more active, creative, and independent in their learning while still maintaining the rich heritage of Kemper for its quest of excellence in education.