The word "helpmeet" goes back, of course, to the KJV rendering of Gen. 2:18, where it was intended to be a noun "help" and an adjective "meet" (= suitable). On the history of misunderstanding produced by this rendering, this is helpful (pp. 216-17).
But actually the same rendering is found before the KJV (1611), in the Geneva Bible (1587): "an helpe meete for him." This is apparently the first English translation with this rendering. The Bishops Bible (1568) has "an helpe lyke vnto hym," and its predecessors (Wycliffe, Coverdale) rendered generally similarly.
The first recorded use of the two words as a compound noun is in Dryden's play Marriage a la Mode (1673), Act 4, Scene 2. However, the online text of Dryden's play doesn't contain the word, but gives instead "help-mate," as mentioned in the article linked above. Here's the paragraph as contained in this text.
_Rho._ [_Aside._] She's sick as aptly for my purpose, as if she had contrived it so. Well, if ever woman was a help-mate for man, my spouse is so; for within this hour I received a note from Melantha, that she would meet me this evening in masquerade, in boys' habit, to rejoice with me before she entered into fetters; for I find she loves me better than Palamede, only because he's to be her husband. There's something of antipathy in the word _marriage_ to the nature of love: marriage is the mere ladle of affection, that cools it when 'tis never so fiercely boiling over.