St Mary's Collegiate Church Youghal is a building of very remote antiquity. It is one of the oldest churches in the country and occupies a site devoted to religious worship since early Christian times. The building is now a National Monument of unparalelled historical importance for Ireland.

The church is likely to have been a monastic settlement of Saint Declan of Ardmore (c450). It was rebuilt in Irish Romanesque style (c750) and the Great Nave was erected in the year 1220. The early 13th century re-building was under the direction and hand of the Masters of four local guilds of operative masons, whose marks are to be be found on the pillars of the gothic arches.