The origin of Blackjack is somewhat unclear. Some people believe that Blackjack originated in French casinos in the early 1700s where it was known as "vingt-et-un" ("20 and 1").
The game became known as Blackjack because if a player held a Jack of Spades and an Ace of Spades as the 1st two cards, the player was paid out extra. So with a Jack being a vital card and Spades being black, the game was called Blackjack.

This game has been played in the United States since the 1800's. However, between the 1850's and 1910, gambling was legal in the United States until Nevada made it a felony to gamble. In 1931, Casino gambling was re-legalized in Nevada where Blackjack became one of the main games offered to gamblers.