Have any real people been de-canonized? People can be canonized (declared to be saints) and these official declarations are held to be infallible. Some people might be considered saints because of popular devotion, without being actually canonized - they could be "grandfathered in," rather than going through the modern process. I am aware of instances where the Church has decided that some of these people are of dubious historicity and therefore are not actually saints. 

Examples:


St Guinefort, who was not only fictional, but was also a dog. 1
St Josaphat, whose story is a fanciful version of the life of Buddha (Josaphat = Boddhisatva). Yes, Buddha existed, but the Josaphat story is not historical. 2


Has the Church ever declared "X should no longer be considered a saint" where the reason isn't "because X never existed"?

1: It's like the end of Lady and the Tramp, but seven centuries ago.
2: Also, Wikipedia is wrong to say that he was canonized: he appeared in the Baronius Martyrologium Romanum but Benedict XVI's De servorum Dei beatificatione et beatorum canonizatione says that doesn't imply canonization.
Technically&hellip; no. The Catholic Church has never decanonized a saint in the sense of saying, "This guy used to be a saint, and now he's not." But the reason is actually quite fascinating. 

Canonization doesn't actually make someone a saint, per se. A Catholic "canonization" is the process by which the Church ultimately recognizes something God has already done. The Catholic Church does not claim that all "saints" (in the eyes of God) have been canonized, but they do say that an authentic canonization is both infallible and irrevocable. 

In the early 1980s, the Catholic Church made some huge changes to shore up the canonization process. In centuries past (starting in about the 10th century), many of the claims of sainthood were adopted from ancient times, largely through public acclaim and popular stories passed through long-standing tradition and legend. Finally, higher authorities (and eventually the Vatican) took over the process of formally authenticating sainthood.

So what's been going on in the last several decades is the Catholic Church as been meticulously examining the authenticity of some 10,000(?) named saints spread through official sources, local martyrologies, and other historical archives to authenticate if a canonization ever actually took place.

Over the centuries, there were a lot of claims of sainthood without any verifiable authenticity. Several stories of sainthood turned out to be multiple references to a single person. There were mistaken identities, and in many cases, historical figures simply could not be separated from local folk tales and legends. 

The more rigorous authentication does not imply a lack of veneration. After 2,000 years, the Church is simply saying that they cannot authenticate the events of veneration, or even if the person actually existed &mdash; thus, claims of canonization cannot be authenticated.

But no one has ever been "decanonized", even if such a word could exist.