The Parish is composed of the Union of Sandyford and Glencullen, so called from the situation of the two churches. It was formerly a part of Cabinteely parish and was administered by a curate William Flood whose residence was at Sandyford. Rev Patrick Smyth was appointed to take over the curacy in the month of October 1823.

By 1829 the district of Sandyford that adjoined Cabinteely was formed as a distinct Parish in its own right by the then Archbishop D Murray. On April 6 th 1829, the Archbishop appointed that curate who had taken care of Sandyford during the time of its union with Cabinteely, namely, Patrick Smyth as Parish Priest.

Fr Patrick Smyth PP of Sandyford very quickly with the help of generous benefactors managed to finally give to Sandyford Church the finishing touches it was so long without. Although St Mary’s Church was dedicated in 1806 and called the Church of the “Assumption of the Blessed Virgin Mary” it had remained unfinished. The new Parish Priest Fr Smyth faced the challenge of the T shaped church having no vestry, no good vestments nor a decent existing chalice.

Fr Smyth’s agenda was to build on the work of his predecessor, Rev. William Flood, and see the church to a reasonable state of completion to enable public worship. The church was roofed in 1830 by the generous contributions of B.C. Lawless who financed the project. It must be noted that although unroofed before this date people still gathered for mass in the barn like church.

By 1832 Fr Smyth set about providing a suitable residence in the grounds and by then was sent his first curate Rev T.A. Murphy.

By 1840 the urgent need for schools in the parish was met, thus far the education of the young had taken place in the church. This was made possible by the partial estate of a Lord Castlecoote who upon his passing left a significant sum, covering the cost of Sandyford School at lamb’s cross, comprising of two separate buildings, one for boys and one for girls; a similar construction was erected in Glencullen. These would be replaced by the current buildings respectively in 1936 and 1945.

By 1840 too the tower spire and vestry were in place bringing St Mary’s closer to its present shape . Fr Smyth added a library in one of the church porches indicating his concern to improve the minds of the people.

By 1845 Rev P Doyle who had provided support to Fr Smyth during a pilgrimage break to Rome was asked to remain on in the parish, taking up residence in Glencullen in a house adjoining the church there.

The Parish Priest now having two assistant priests conducted a census of his flock in 1853 showing a total of 2554 Catholics.

Fr Smyth died on 28 th May, 1860 and is buried in Glencullen.