The Civil Parishes were the major administrative division until 1898. Therefore, becoming important civil divisions in their own right. The Ordnance Survey completed in 1846 contains maps at the scale of six inches to the mile of each of the 60,462 townlands in Ireland. Townlands are grouped into Civil Parishes, which are grouped into Counties, which are grouped into provinces. The boundaries of the diocese have remained constant and are used by both the Roman Catholic and Anglican churches.
Diocese boundaries have no relation to county boundaries, however.
In 1858 a principal registry and eleven district registries were established to prove wills and granting administrations. The boundaries of these districts were either baronies or counties. Detailed maps were made of many estates in Ireland. They are indexed both by place and by person. You will only find them in a large library.