From Paul Johnson’s The History of the American People (p. 97f):
The venom of New York politics led to America’s first trial for seditious libel in 1735, when John Peter Zenger, who had founded New York’s Weekly Journal two years earlier, was locked up for criticizing the governor, William Cosby, and finally brought to trial after ten months behind bars.
(…)
It is significant that Zenger, or rather his lawyer, Andrew Hamilton of Philadelphia, put forward truth as his defense. That would not have been admitted in an English court where anything was criminally libelous whether it was true or not, which fostered ‘an ill opinion of the government.’ Indeed, it was an axiom of English law, in seditious libel, that ‘the greater the truth, the greater the libel.’ In Zenger’s case the judge tried to overrule his defense, but the jury acquitted him all the same – and that was the last of such prosecutions.
More on seditious libel here. Here is the first report on the trial.