St. Mary's Church of the Assumption in Tullamore was first erected on this site in the year 1802. The old church was demolished in 1902 an a new Gothic style Church erected to a design of the architect William Hague. Work on the present church actually commenced in 1898 and was completed by 1906. This Church was destroyed by fire on the 31st of October 1983. Work on this new Church commenced soon afterwards and the first mass was said here on the 9th of August 1986 by Reverend Patrick Fallon P.P. The design of the new church was under the supervision of Edward N. Smith, architect and was built by John Flanagan & Sons of Tullamore.

As much as possible of the fabric of the old church, including the famous Tullamore stone-work, was incorporated in the new church and at the time two transepts were added to give a cruciform shape with the sanctuary and sacristy located at the western end instead of the eastern end so as to provide seating on three sides of the sanctuary.

One of the main features of the interior is the self finished timber ceilings and laminated structural frames. The steeply pitched main structure portal frames are reminiscent of the high lofty ceilings of the old church. The sanctuary furnishings including the altar, ambo, sedes and seating are of Caen Stone and suitably embellished with exact replicas of carvings from The Book of Durrow. The reredos is of travertine marble, highlighted with the Twelve Apostles in high relief.

Special features of the church are the stained glass windows over the high altar, and in the tow transepts. These windows depict scenes from The Resurrection, The Annunciation and the Nativity. Windows from Harry Clarke Studios and formerly with the Jesuit Community in Rathfarnham Castle were donated to the parish as were The Stations of the Cross from St. Patrick's College
Drumcondra while the baptismal font is from the old Church of Ireland church of Lynally, Tullamore - a gift of the Church of Ireland parishioners.

In 1994 work was completed on the church organ. This organ was originally built by the firm of Thomas Frobenius of Copenhagen and was donated to the parish by the Council if the Congregation of the Cathedral of Copenhagan (The Church of Our Lady - Vor Frue Kirke). The organ was reconstructed in Tullamore by a team from Thomas Frobenius of Copenhagan and under the guidance of Professor Gerard Gillen on behalf of the Parish.

The black wooden cross in the day chapel was constructed from charred remains of the old church while the mosaic of Our Lady with the veil is all that is left of the mosaic tiling which surrounded the main altar of the old church.

In the porch of the day chapel is a painting by Oliver Connolly of the Exterior of the old church. Available from OHAS, Bury Quay, Tullamore are copies of Tullamore Catholic Parish; a historical survey and Durrow in history both books providing further details of the history of the parish, its churches and parish life.