Off To KinderhookOK may have gone into Obscurity had it non been for Martin Van Buren, the democratic candidate in 1840. Martin Van Buren was the current president. The Campaign for re-election captured the craze of saying Ok and associated it with Martin Van Buren's home town: Old Kinderhook, New York. This was a catchy way to remember to vote for Van Buren was a vote for OK. The Whigs re-incorporated OK to a new meaning for the departure of the current president. The Whigs flaunted the departure of Van Buren with the saying "off to Kinderhook."
The Myth around OK is fascinating and has a number of stories connected to it. As far as The Merriam-Webster New Book of Word Histories knows, the Martin Van Buren campaign was the biggest influence on this use of that word.
“Some people wear their smile like a disguise. Those people who smile a lot, watch their eyes. I know 'cause I'm like that a lot. You think everything's ok, and it is . . . 'till it's not.” Ani Difranco quotes
Ngram PopularityOK is currently at its height of popularity.
The Merriam-Webster New Book of Word Histories ( Miriam Webster Inc., 1991), 329-331