On at least eighty-seven occasions between 1789 and 1901 the Canadian state authorities made the dramatic move of setting aside days so that their populations could thank God for blessings, or implore His intervention and assistance in periods of crisis. Before Confederation every Canadian colony and province had developed a tradition of marking exceptional occasions with days of fasting and thanksgiving. After 1867 provincial governments, and then the Dominion government, would regularly call thanksgiving days for good harvests. Improvements in communication from the 1880s made the first genuinely empire-wide days of prayer possible. This article considers why days of fasting, humiliation and thanksgiving were such an enduring aspect of nineteenth-century Anglo-Canadian life. Special acts of worship would change their character and purpose over the course of the century, but they survived because Protestant churchmen and civil officials continued to value their community-building potential. The doctrine of “national providentialism” – the idea that nations and peoples were rewarded or punished as a collective for their piety and sinfulness – nourished a range of community identifications in pre- and post-Confederation Canada. On the one hand the essay explores the varied senses of community that were stimulated by imperial, dominion, provincial and regional holy days; on the other, it shows how these occasions could expose fault-lines in Canadian society. Clergymen often struggled to make their congregations feel responsible for, and unified with, communities and sufferers elsewhere. And days that were intended to appeal to everyone were associated with Protestantism and a British reading of Canadian nationality.