A few random observations, in no particular order:
Scott Naylor’s Ottawa Area Grave Markers gallery is a wonderful source of headstone photographs, covering many cemeteries (both Catholic and Protestant) on both sides of the Ottawa river (i.e., on both the Ontario and the Québec sides of the Ottawa Valley area). And he is continually adding more cemeteries. I was surprised (and delighted) to recently discover that the site now covers Notre Dame, Ottawa: a huge, and densely populated, cemetery. I can’t even imagine the hours of unpaid work put in by dedicated volunteers: it is a gift to the public (or to that subset of the public that has an interest in genealogy), for which I am very grateful indeed. I’ve found ancestral markers there that I hadn’t realized even existed: I knew (from parish registers and/or civil death records) that the ancestors had been buried at Notre Dame, but I hadn’t known about their headstones.
The headstones in any given cemetery may represent only a portion of those buried there. Or, to put it another way: some people were buried without a headstone. For the nineteenth century (not to mention earlier than that), many people, actually. Headstones were expensive; and for humble folk, much closer to a luxury than a necessity.
In my family, a “decent burial,” with a three-day wake and a proper mass and all of the trimmings, was considered a necessary endpoint and a well-earned tribute, with anything less than that seen as an insult to the memory of the deceased, and a real source of shame to the family. But a costly, fancy headstone was not expected, and was probably seen as something like icing on the cake.
For my nineteenth-century Ireland-to-Canada ancestors, I’ve found that the existence of a headstone is more the exception than the rule. And while I haven’t done the math with a systematic statistical survey or anything like that, I’d be quite comfortable in asserting that well over half were buried without a headstone, and would further estimate that it was over 75 percent. Moreover, this “buried without a headstone” practice continued for a couple of generations at least, until the early twentieth century. Your mileage may vary, of course, depending on the socioeconomic status of your ancestors, and their religious affiliations and cultural practices, and so on.
If you’re looking for RC burials in the nineteenth-century Ottawa Valley area, the parish register is your best friend, or at least your best source of information. Remember that the civil registration of deaths in Ontario wasn’t instituted until 1869, and that it took a generation or two before anything close to full compliance with the demands of the civil authorities. Sometimes the church records will give you information that never was recorded by the provincial government in the first place. But also be aware that in the early days of RC parish formation, the priests were basically circuit riders visiting various missions on horseback at irregular intervals, and that they missed a lot of burials: while baptisms and marriages could be put on hold until the next time the priest came around, the body had to buried (and often without any record, whether civil or ecclesiastical, whatsoever).
Earlier burials can sometimes be reasonably inferred from the records of later burials. I don’t know for certain that my 3x great-grandfather James Moran (died ca. 1857) was buried at St. Michael’s RC Cemetery in Corkery, but I have reason to suspect that he is buried under that sod. His widow Margaret Jamieson was buried there (but without a headstone) in 1882, according to the parish register. The practice was to bury a widow or widower next to his/her deceased partner (just one of several reasons why remarriage after the death of a spouse was somewhat frowned upon in my family: but where would the new spouse be buried? and what about the long-suffering, if long-deceased, first wife or husband?).
The information on a headstone, while carved in stone, should not be taken as, well, carved in stone. I’ve seen errors not only in birth years (understandable enough, for those who lived and died in an era before widespread literacy, and before a Hallmark greeting card emphasis on the sentimental significance of birthdays), but in death years, too (and I’m talking twentieth century here, by the way). Don’t assume that a headstone was erected the day or two after an ancestor’s burial. Sometimes a decade or two had passed before someone got up the money or the inclination to commission a headstone, at which point the dates and the details may have become a bit fuzzy.
The discovery of a headstone for my great-great-grandmother Bridget Galligan, who died in childbed in 1861, really smashed open a brick wall for me. I first encountered evidence of her burial at Scott Naylor’s above-linked Ottawa area grave marker gallery, but the photograph below is my own, taken on a snowy day in January. The headstone, from St. Michael’s RC Cemetery in Corkery, Huntley township, identifies her origins not only in terms of the the County of Cavan, Ireland, but more specifically in relation to the parish of Kilmore.