There had been a number monastic bishops at the abbey, but it was not until the Synod of Rathbreasail in 1111 that the diocese of Clonard was established.
Its boundaries were set at the Synod of Kells in 1152, which covered roughly the western part of the Kingdom of Meath with the diocesan bishop's seat (cathedra) located at Clonard Abbey.
Clonard acquired most of Magh Breagh (what is now the county of Meath) by absorbing the diocese of Duleek later in the twelfth century.
In the Roman Catholic Church, Meath is still a separate diocese.
The Roman Catholic bishop's seat is located at Christ the King Cathedral, Mullingar.