Assumption Catholic Church 115 W 3rd St, O Fallon, MO63366 Assumption Catholic Church was established in O'Fallon in 1871 by a small handful of families in the area.…More Today the church congregation has grown to nearly 3,200 families and is the third largest in the archdiocese of St. Louis. A second church was built in 2005 to accommodate its growing membership and is connected to the original at 115 West Third Street. The church mission states: "May you find Christ here--may you bring Christ to the world." It offers several programs for youth including child care during mass, Sunday pre-school and Extreme Teen Ministry. It is also involved in several projects to help those in need both locally and worldwide. Assumption offers small Bible study and prayer groups, women's and men's retreats and several programs geared towards members' special talents and interests.