Barry Griffin posted this today in the Facebook group "Irish Genealogy":

I map all the surnames for the 1901 and 1911 Irish census. I have now also added maps for each surname showing the distribution for Catholics, Presbyterians and Anglicans. People of Native-Irish and Norman-Irish extraction tend to be Catholic, Scots-Irish (Ulster-Scots) are typically Presbyterian or Anglican, and Anglo-Irish are usually Anglican.

Click here to link to Griffin's website.