The first settlers came to the O’Fallon area in the late 1700’s. It was during this time that Fort Zumwalt was built as a trading station and as a protection for the settlers. O’Fallon began, officially, in 1856 when Nicholas Krekel, a federal judge for western Missouri, built a house in the woods along the North Missouri Railroad on land owned by a friend, Colonel John O’Fallon.
In the fall of 1869, seventeen farmers, all parishioners of All Saints Parish in St. Peters, met to discuss the possibility of building their own school and church in O’Fallon because of the great distance to St. Peters. The Church of the Assumption of the Blessed Virgin Mary and the log schoolhouse were completed and dedicated on September 17, 1871. A week later the school opened to twenty pupils.
In September, 1873, the Sisters of the Most Precious Blood were assigned to the school and continued their service to Assumption, uninterrupted, until 1991.
An accredited junior high school was opened in 1923, and was housed in the library of the elementary school. From 1923 to 1929, Assumption operated as an elementary school with a junior high school. The enrollment of Assumption School was, by 1929, three times its capacity.
In 1929, a new high school building was dedicated. In 1930, the old church was razed and the present limestone building begun.
The building was dedicated in 1955 as Assumption High School. As the growth of the county continued, the Archdiocese made the decision to build a regional high school. With the dedication of St. Dominic High School, Assumption High School was closed in 1962. With the Assumption High School available, the Elementary School moved in, with the previous elementary building becoming the Early Childhood Center where Pre-Kindergarten programs were provided.
A new church and parish hall was dedicated on February 26, 2005. The Elementary building was expanded to include several new classrooms, two science labs, and a Resource Room in 2013. In 2016, we began a Montessori program that is housed in the Early Childhood building along with our Pre-Kindergarten and Kindergarten programs.