It's certainly not The Joy of Sex, but Aristotle's Complete Master-Piece, published in 1766, has been credited as the first sex guide to be published in America. A read of some excerpts certainly fills one with the feeling that despite the sad state of affairs that is sexual education in the United States right now, at least we're not still referring to penises as "the Yard."
The book is actually older than its pre-Revolutionary war publishing date as seen here; it was put out, in varying forms in England as far back as 1507. Here are few choice passages.
Virginity untouched and taintless, is the boast and pride of the fair sex, but they generally commend to put it off; for as good as it is, they care not how soon they are honestly rid of it. And I think they are right; for if they keep it too long, it grows useless, or at least loses much of its value, a stale virgin (if such a thing there be) being looked upon like an old almanack out of date.
...the holy Jesus has told us, That in the beginning it was so; the marriage of one man to one woman: so that as these conjugal delights cannot be enjoyed but in a married state...And it is in the breaking of this order that has filled the world wiith confusion and debauchery, has brought diseases on the body, consumptions on estates, and eternal ruin to the soul, if not repented of. Let therefore either sex, that have a desire to enjoy the delights of mutual embraces, take care that they do it in a married state with their own wives or husbands, or else it will become a curse to them instead of a blessing...
And a definition of the "Clytoris":
a sinewy and hard part of the womb, replete with spongy and black matter wihin, in the same manner as the side ligaments of the yard: and indeed resembles it in form, suffers erection and falling in the same manner, and it both stirs up lust, and gives delight in copulation: for without this, the fair sex neither desire mutual embraces, nor have pleasure in them. nor conceive by them: and according to the greatness or smallness of this part, they are more or less fond of men's embraces; so that it may properly be stiled the seat of lust.