In 1248 a private chapel was built within the Fitzgerald Castle site.

It was established as a prebend to Dublin’s St. Patrick’s Cathedral which shows the influence of the Fitzgeralds at that time.

The current building on the same site is a detached six-bay double-height rubble stone Gothic-style Church of Ireland church, built 1859, incorporating the fabric of earlier chapel on the site.

The Tower adjoining St Marys Church of Ireland is the sole surviving section of the 1580 Maynooth College.

The third duke Agustus (1791-1874) assumed the dukedom in 1814,  he is buried in the Tower and he was the first titled FitzGerald to be buried in Maynooth. Among other things he was Grand Master of the Freemasons Grand Lodge of Ireland from 1813 until his death in 1874, a tenure of 61 years. Showing his esteem among his peers.

The fourth duke opened the family private cemetery in Carton.

St. Mary’s is part of the Meath and Kildare Diocese and is still in use today.