Ben Zimmer has antedated the title "Ms." to 1901.
On page 4 of the Springfield (Mass.) Sunday Republican of November 10, 1901, under the heading "Men, Women and Affairs," is the following item, in which the writer suggests that "a void in the English language" may be filled by Ms., pronounced as "Mizz," as an alternative to Miss or Mrs.He also cites a far earlier example of Ms. used an an abbreviation.
Some have theorized that Ms. has roots long before the 20th century. One piece of evidence that has been put forth is the tombstone of Sarah Spooner, who died in 1767 in Plymouth, Massachusetts. As you can see from this image, what appears on the headstone is M with a superscript s. As Dennis Baron writes in his excellent book Grammar and Gender (1987), "it is certainly an abbreviation of Miss or Mistress, and not an example of colonial language reform or a slip of the chisel, as some have suggested." [Link]