St. Mary's Parish traces its beginning back to the turn of the century. In 1906, Pope Sait Pius X ordered the establishment of the Confraternity of the Christian Doctrine in every parish throughout the world. Two years later, one of the original church committeemen arranged for a religion teacher to come from Pittsburgh to Cecil on Sundays. St. Mary's was the first CCD center in the Diocese. This led to a petition from the people in Cecil to form their own parish, which was done in 1909. St. Mary's officially began with the document dated February 12, 1910 in which Bishop Regis Canevin separated the villages of Gladden, Reising, Bishop, and Cecil from the parishes of St. Agatha's and St. Barbara's in Bridgeville to the new parish of St. Mary of the Assumption. The cornerstone of the first church was laid on Labor Day, September 6, 1910 and was dedicated by Bishop Canevin on May 1, 1910.

The Assumption Hall was dedicated in November 1956, and it was used as a temporary church during construction of the new church, which was built on the same site as the original church.

The new church, dedicated April 28, 1963, has been hailed as a "marvel of outstanding design". The Structural Clay Products Institute named the church as an "excellent example of tasteful use of brick" as well as the "use of prestresses concrete panels for the roof". Each is some 23-feet long, nine feet wide, and weighs about eight tons. The altar is hand-hewn of marble, cut from a single three-ton block in Italy and shipped to Pittsburgh. Stained glass is of a facetted-type in an abstract design. The two big windows in the church serve as a memorial to the women of the Altar Society and the men of the Holy Name Society for the many hours they gave and the thousands of dollars they raised so that future generations would have a beautiful church in Cecil.