"There's a sucker born every minute" is a phrase closely associated with P. T. Barnum, an American showman of the mid-19th century, although there is no evidence that he said it. Early examples of its use are found instead among gamblers and confidence men.
Attribution to Barnum
When Barnum's biographer, Arthur H. Saxon, tried to track down when Barnum had uttered this phrase, he was unable to verify it. According to Saxon, "There's no contemporary account of it, or even any suggestion that the word 'sucker' was used in the derogatory sense in his day. Barnum was just not the type to disparage his patrons."
Some sources claim the quote is most likely from famous con-man Joseph ("Paper Collar Joe") Bessimer, and other sources say it was actually uttered by David Hannum, spoken in reference to Barnum's part in the Cardiff Giant hoax. Hannum, who was exhibiting the "original" giant and had unsuccessfully sued Barnum for exhibiting a copy and claiming it was the original, was referring to the crowds continuing to pay to see Barnum's exhibit even after both it and the original had been proven to be fakes.
Another source credits late 1860s Chicago "bounty broker, saloon and gambling-house keeper, eminent politician, and dispenser of cheating privileges..." Michael Cassius McDonald as the originator of the aphorism. According to the book Gem of the Prairie: Chicago Underworld (1940) by Herbert Asbury, when McDonald was equipping his gambling house known as The Store (at Clark and Monroe Streets in Chicago) his partner Harry Lawrence expressed concern over the large number of roulette wheels and faro tables being installed and their ability to get enough players to play the games. McDonald then allegedly said, "Don't worry about that, there's a sucker born every minute."
Early uses of the phrase refer to it as a catch-phrase among gamblers. In an 1879 discussion of gambling in Chicago, an "old-timer" is quoted as saying, “[G]oodness knows how they live, it’s mighty hard times with the most of them; in the season they make a bit on base ball, or on the races, and then, you know, ‘there’s a sucker born every minute,’ and rigid city legislation drives the hard-up gambler, who would be a decent one of the kind, to turn skin-dealer and sure-thing player.” The use of quotation marks indicates that it must already have been an established catch-phrase.
The phrase appears in print in the 1885 biography of confidence man Hungry Joe, The Life of Hungry Joe, King of the Bunco Men.
In a slightly different form, the phrase shows up in the January 1806 European Magazine: "It was the observation of one of the tribe of Levi, to whom some person had expressed his astonishment at his being able to sell his damaged and worthless commodities, 'That there vash von fool born every minute.'"
According to David W. Maurer, writing in The Big Con (1940), there was a similar saying amongst con men: "There's a mark born every minute, and one to trim 'em and one to knock 'em." Here "trim" means to steal from, and "knock" means to persuade away from a scam. The meaning is that there is no shortage of new victims, nor of con men, nor of honest men.
In the 1930 John Dos Passos novel The 42nd Parallel, the quotation is attributed to Mark Twain.