Grammar Girl says she regularly gets questions about the differences between till, until, and 'til, and how to use them.
I say: ????? And when exactly did this "'til" thing come about?
'Til is apparently in the process of becoming accepted (shudder), but it is a totally unnecessary word. I think I know what happened: somewhere along the line people began to assume that "till" (as they heard it pronounced, not necessarily as they spelled it) was an abbreviation for "until," and they couldn't figure out why you wouldn't spell that as 'til. But till and until are actually separate words that are synonymous. Yes, till is a noun meaning cash register and a verb meaning to work the ground (lesser known, it's also a noun meaning a glacial drift or a stiff clay), but its #1 function and definition in my dictionary is as a preposition meaning "up to the time of; before; until." Of the two words, till is actually older. Until came later. 'Til came, well, way, way later, and, I believe, under mistaken circumstances. We don't need it. We already have the one-syllable form till, which is not an abbreviation.
The Associated Press Stylebook recommends till or until, but not 'til. Bryan A. Garner, of LawProse calls 'til a "little virus," and his quotes of several other usage guides includes this: "'Til is a variant spelling used by those who think (incorrectly) that till is a clipped form."
I'm pretty open to changes in the English language. I'll go pretty far with verbing nouns, and I think "they" and "them" will become standard singular pronouns for a person of unknown gender within my lifetime. But 'til -- nah. It's going to be a long time till I can go there.