The first recorded use of the gender-inclusive title Mx in print, from The Single Parent magazine, volume 20, April 1977.
The letters page âIn The Chaptersâ by Ann Parks, page 21, gives some context - it appears that a previous issue had asked a question to which Mx was one of the suggested answers:
There has been some response to the question of what to call men and women (other than Mr. and Mrs./Ms.). Â Exâhusbands are WASbands, of course. Â Pat Kite (Single-Again Scrapbook, April SINGLE PARENT) felt that both sexes should be designated MX. Â But Dalynn Hoeflin (Solano County, CA 92) feels that males should be
But the actual first use in print is on Page 16 in an article called âSingle-Again Scrapbookâ by Pat Kite. This appears to be a short story, possibly part of a serial, involving a flirtatious encounter at a party:
âTHE WORST PROBLEM facing the single woman today is having to decide whether she is Miss., Mrs., or Ms.,â said the Blue-Eyed Man as he sat sipping his rosĂŠ.
 âOoohh, really?â I gasped, swallowing my frito whole.
 âIâm glad you agree,â nodded the Man, taking the matches from my hand to light my cigarette. âNow, where I work we make it a point to call every female âMs.â  It took me quite a while, but I made it.  Now everybodyâs happy.â
 âWhere do you work?â I asked.
 âThe welfare bureau.â
 âDo you mean if you get a widow who was married forty-eight years in your office, and you address her as Ms., she likes it?â
 âWhy not?â said the Man.
 âFrankly the term Mizzzz reminds me of the servant section of a pre Civil War Southern plantation,â I commented, drawing out the words through clenched teeth.
 âOh, that was in the pastâ smiled the happy Man. âNow Ms. for everyone connotes individuality.  What tile do you go by?â
 âMrs.â I replied with a shrug.
 âBecause I have four children and I like them to look legitimate, thatâs why. Anyhow, if Mrs. and Miss are to be shortened to Ms., then I think Mister and Master should be changed to Muster ⌠abbreviated Mu. On second thought, maybe both sexes should be called Mx.  That would solve the gender problem entirely.â
 âAre you a womenâs libber or something?â said the horrified Man.  "Then how come you didnât get mad when I lit your cigarette?â
 "Because it was a gesture of courtesy,â I answered, âand I donât think good manners ever go out of style.  Besides, I love having doors opened for me, and my heavy packages carried.â
 âOh, then youâre not a libber!â said the Man with a sigh of relief.
 âIt all depends on how you look at it,â I replied.  "For instance, if youâll give me my matches back, Iâll be able to light your cigarettes.  We could take turns.â
 "You wouldnât.  .  .  .!â
 âWhy not?â I said with a tiny smirk.
 âYou know, the biggest problem women have today is whether to be Miss, Mrs., or Ms.,â said the Man, as he took the matches from his pocket and lit my Bel-air.
 âNot quite, kind Sir,â I commented, trying to change the topic to the artistic merits of Alice Cooper.
 "Yes really, Ma'am,â laughed the Man as he got up to dance.
 And we mixed our whimsey with our wine until well past midnight.â
There are also a number of examples of people discussing Mx on Usenet newsgroups starting from 1982, with the first person mentioning that they have used the title for themself appearing in 1998.
Mx is currently being considered for inclusion in the next edition of the Oxford English Dictionary.
(Thanks to Alex from Nonbinary Inclusion Project and several Twitter users, including Altivo, who helped a great deal in tracking down this article.)