The Parish of St. Agnes was founded in 1887, when the first Mass was celebrated at Walter Johnson's blacksmith shop with an anvil as the altar.

By 1890, the blacksmith shop could no longer accommodate the parishioners so a small group rented the Gildersleeve's Hall in the local Institute Building.

Due to the increasing number of parishioners, the small marble church grew insufficient for the needs of the parish, so demolition began in 1933, under the direction of Msgr.

In 1935 the current building was completed and in 1957, Pope Pius XII announced the formation of the Diocese of Rockville Centre and appointed Most Rev.

1981 saw a major facelift for the aging building and while the cathedral was being renovated, daily Mass was celebrated in the Episcopal Church of the Ascension located across the street.

Guglielmone was subsequently named bishop of the Diocese of Charleston, South Carolina and was ordained and installed on March 25, 2009.

The rector of that time (Monsignor Edward Melton) was concerned with maintaining the parish schools so an electronic organ was temporarily installed.

A small Moeller pipe organ was located in the 1960s and 70s near the Blessed Sacrament Chapel and later moved to the Lower Church.

To mark the Jubilee Year of 2000 plans were made to build a new pipe organ for St. Agnes Cathedral Parish.