By 1950, St. Patrick's Church, founded in 1933, had over five hundred Catholic families. The decision was made to start a school.

The Cash Farm on the corner of Moseman Road and Hanover Street was purchased and the farmhouse converted into classrooms by parishioners. The Missionary Sisters of the Third Order of St. Francis of Peekskill were enlisted to teach and Sr. Mary Robert became the first principal. Construction of a real school building began in 1952, but it was not ready in September of 1953, so a partition was put up to divide the church hall into two rooms. Sr. Mary Robert taught forty students in grades 3 and 4 in one room, and Sr. Ann Michael taught fifty students in grades 1 and 2 in the other!

What is now known as "Building A" was completed early in 1955 along with a gymnasium. As the classes grew in size, "Building B" was erected in 1959. That same year witnessed the building of a convent so the Sisters would no longer have to commute each day from the motherhouse in Peekskill. By the end of the 1950's the enrollment soared past 500!

By 1960 the parish had 2,000 registered families, so the archdiocese decided to establish a separate parish in Shrub Oak. In June of 1963, St. George's became the parish of Blessed Elizabeth Ann Seton and a whole new church and school complex was begun under the leadership of Msgr. Arthur Nugent. Its families numbered 300, while 1,450 stayed with St. Patrick's.