Keno's roots are in China, and the game was brought to the United States by Chinese immigrants in the late 1800s. It was originally played with 80 Chinese characters, which in the United States were replaced by 80 Arabic numerals.
For a time in Nevada, each number was accompanied by the name of a racehorse, and the game was known as racehorse keno. The horses' names disappeared in 1951, when a tax on off-track betting on horses was passed. Operators didn't want their game mistaken as betting on the horses. Still, remnants of racehorse keno games remain. Many casinos still call each game a "race" -- if you bet on more than one game at once, you buy a multirace ticket.
Almost all Nevada casinos have keno lounges, where numbered balls are forced out through an air blower to determine the winners. Some tribal casinos in the upper Midwest also have live keno lounges, and Atlantic City began offering live keno in 1994. On riverboat casinos, keno enthusiasts play video versions, which have grown in flexibility and even offer bonus rounds in the video slot age.