Ask many a grade-schooler (and many an adult, for that matter) what animal the korban pesach is, and he'll tell you "a sheep".^[1]

In fact, it can be a sheep or a goat. (It's explicit in chumash (pesach MItzrayim) and halacha (pesach doros).)

Do we have some tradition (or historical evidence) that it was usually a sheep? If not, how did it happen that people associate the korban with a sheep?

^[1] I have no empirical evidence to offer as far as asking people: it's just my impression. But all I can find using Google (that discusses the pesach as a goat without mentioning that it can be a sheep) is discussing individual cases in which someone brought a goat (including, of course, the case in parashas Tol'dos), plus one blog post. On the other hand, there is much mention of the pesach as a sheep without mentioning that it can be a goat; see e.g. a vbm-torah.org article and a torah.org article.