1798:  The first Catholic church in Collooney after Penal Days was built on the site now occupied by the Church of the Assumption.  The parish historian, Archdeacon O'Rorke, who would have known it well, calls it "a substantial slated building", but goes on to admit that it was "a humble structure in itself."

1843:  The earlier building was removed to make way for the present fine Church of the Assumption.
The Sligo Champion on 14th January 1843 noted under the heading COLLOONEY CHAPEL, "The walls of this chapel are nearly finished, and it is expected that a roof will be put on in March." It seems safe to assume that the parishioners began to worship in the church in this year.

The architect of the church was Sir John Benson, a native of Collooney. The style is early English Gothic. The Parish Priest, who was the driving force in seeing that the church was built, was Dean Patrick Durcan who later became bishop of the diocese.