One of the most useful bits of information that the Canadian census can supply is that of the religious affiliation of your ancestor(s). This is worth knowing not only as an interesting and sociologically significant detail about the life of your ancestor, but also as a guide to further sources (church records, cemetery records, and so on).
However, you may come across an entry in the Religion column of the Canadian census that doesn’t immediately make sense to you, perhaps because the enumerator used an abbreviation that is no longer in common use, or perhaps because he used his own version of a shorthand designation.
For example, you may come across an ancestor, let’s say born in Upper Canada of Scottish origin, whose religion is listed as FC. What does that FC mean? The FC stands for Free Church, or Presbyterian. Or it may be FK, for Free Kirk (Scottish for Church, also Presbyterian). Or perhaps you’ll find an ancestor, born in Ireland and therefore of Irish origin, with religion listed as English. That English refers to the Church of England, which means that your ancestor was enumerated as an Anglican. Or maybe your ancestor was born in Ontario of Irish origin, with religion listed as C. Rome. C. Rome stands for Church of Rome, or Roman Catholic.
Library and Archives Canada has a very brief list of religious abbreviations here. The Ontario GenWeb Census Project has a more extensive list of religion codes here.
Here are a few of the abbreviations/designations that I’ve come across for Catholic, Anglican, and Presbyterian:
Church of Rome
CR [for Church of Rome]
Papist (actually, I don’t think I’ve seen this in the census, but I’ve certainly seen it in a couple of Ontario civil records).
Church of England
C of E
Church of Scotland