I know humor is often a matter of personal taste, but even with my rather sarcastic sense of humor in mind, I like to think I'd have recognized it in historical fiction if I saw it. To me, it seems much more common in other genres. In romance, it's easy to find examples, from the witty repartee of Regency couples (and these do count as historical fiction in my book, but what of titles outside this category?) to the wacky adventures of many heroines in contemporary romance. There's plenty of humor in mystery, fantasy, sf as I recall. But when it comes to non-genre-crossing, "straight" historical fiction, it seems quite rare. Am I wrong?
Possible reasons for this phenomenon, and more than one could be right:
(1) Historical novelists are a staid, humorless lot. (No, I don't really believe this)
(2) History is a Serious topic, filled as it is with battles, death, pestilence, arranged marriages, class conflict, etc., and adding humor to one of these topics would feel disrespectful and horribly inappropriate.
(3) Many historical novels are either biographical or about particular historical events, and sometimes people's lives (or particular happenings) just weren't funny. Not much you can do about that.
(4) Similarly, many historical novelists use their work to explore the Mysteries of the Universe, the Meaning of Life, and other philosophically deep and profound topics, and those tend not to be funny, either. Or they're not treated as such.
(5) Humor is something that's relatively hard to do well in fiction; it has to come naturally or it just doesn't work. One has to have the personality and writing ability to carry it off.
What else? This is disregarding, of course, the unintentionally funny historical - those with horrible anachronisms, lame dialogue, etc., etc.
Anyway, it has been interesting for me to note some titles I'd read that I thought were truly funny in places, and recognize how often these authors are praised for their unique voice. I enjoyed reading Jane Harris's debut novel The Observations, with its wisecracking, self-deprecating heroine, fearlessly optimistic despite her truly rough past; Bernard Cornwell's The Last Kingdom (and undoubtedly others I haven't read), for his gleefully dry British wit; Karen Mercury's The Hinterlands, which puts its characters in hilarious situations; and James Morrow's The Last Witchfinder, loftily narrated by Newton's own Principia Mathematica, with its sarcastically sly observations on the book world (and which serves as a counterpoint to the sobering main topic of the book, the witch trials of the 17th century). I'll also add Catherine Jinks's incredibly funny medieval novel The Notary, in which the eponymous narrator does his best to keep his lustful nature under control while investigating a murder alongside a Dominican monk. (More on this title later; it's Australian-only, as far as I know.)
Maybe your experience is different from mine, however, and if so, I'd love to hear your recommendations and/or thoughts on the subject. (I believe this topic was touched upon in someone else's blog within the last couple months, but for the life of me, I can't find the relevant entry.)