Yes, of course, jokes are another form of folklore - and so are limericks, slang, jump-rope rhymes, rules of games, urban legends, herbal remedies, recipes, designs of various artifacts and methods of making them, vernacular architecture - and probably you can add to the list. Folklore is whatever knowledge or information meets the criteria that (1) nobody knows exactly who originated it, (2) it gets deliberately passed from person to person, and gets modified as it goes, and (3) it exists in more than one version. (Any of these rules is arguable, of course, but that's the way I see it.)

Since "Pissing in the Snow" has been mentioned. I'd like to recommend a couple of other books:

"Rationale Of The Dirty Joke; An Analysis of Sexual Humor," by G. Legman, 1968.

"No Laughing Matter: An Analysis of Sexual Humor" by G. Legman, 1982.

Legman gets a little heavily into the psychoanalytic interpretation of jokes, but if you want, you can easily skip the interpretation and just read the jokes.

I once read an interesting article in Verbatim - The Language Quarterly, in which the author - a bartender with literary inclinations - treated names and recipes for mixed drinks as a form of folklore. He listed a lot of names of drinks whose names are sexually suggestive (Sloe Screw, Slippery Nipple, etc.) and described how young people are always looking for the mythical drink that will get them drunk without making them sick, causing a hangover, or tasting like alcohol!

Of course, not all folklore is sexual, but sexual stuff is more often folkloric because it has (until recently) been kept out of the mainstream media.