The Earliest Use of the Term “OK” We Have Ever Seen: It also settles the dispute about whether the Democrats and their Whig opponents were referring to Democratic candidate Martin Van Buren as “OK”, as the Whigs used it here to mock him

OK (or okay, and O.K.) is an American word denoting approval, acceptance, agreement, assent, or acknowledgment. OK is used as a loanword in at least 80 other languages. It has been described as the most frequently spoken or written word on the planet. The earliest known use of OK in print was 1839, in the edition of March 23 of the Boston Evening Post, where it was used to mean “all correct”.
It was in an announcement of a trip by the Anti-Bell-Ringing Society. Some later claimed that the term achieved national recognition in 1840, when supporters of the Democratic Party during the 1840 United States presidential election were said to have used it to refer to their nominee, Martin Van Buren, who was nicknamed ""Old Kinderhook"" because he was a native of Kinderhook, NY. Supporters, it is said, held parades with participants shouting “Van Buren is OK”. Others have thrown doubt on the claim of connection to Van Buren. The proof that it does relate to Van Buren is right here before us.

In the 1840 election, voting was held in New Jersey from November 1 to December 2.

A clipping from an 1840 newspaper, likely November, from Warren County, New Jersey, sarcastically entitled “New Jersey, O.K.” giving a report on the failure of the Democratic ticket in New Jersey in the presidential election which pitted Whigs William Henry Harrison against the Democrat (and incumbent president) Martin Van Buren. It is a scornful, mocking article, with such phrases as “The triumph in New Jersey will gladden the heart of every true-hearted citizen of the Union. The Eyes of the Whig Party in every state were turned with intense anxiety toward the theater of the vilest of the machinations of the slaves of executive power [by that they meant the Democrats]. They have been utterly and signally vanquished…the spirit of anarchy and misrule has been powerfully rebuked…not only were the halt, the lame and the blind brought to the polls to support the tottering edifice of locofocoism, but, with singular appropriateness, idiots were brought forward and made to vote in support of a cause, which they, and only they, could sustain without shame now, or reproach hereafter…” The Locofocos were a radical faction of the Democrat Party that existed from 1835 until the mid-1840s. Made up primarily of workingmen and reformers, the Locofocos were opposed to state banks, monopolies, paper money, tariffs, and generally any financial policies that seemed to them antidemocratic and conducive to special privilege. They were anathema to the Whigs. The Whigs won New Jersey by 51.74%. Ads on the back indicate the newspaper was from Warren County, New Jersey.

This is undoubtedly the earliest use of the term “O.K.” that we have ever seen. It also proves that Democrats were indeed referring to Van Buren as OK, so much so that their Whig opponents were used the same term OK to mock him.