As of 2019, how many horses have won the American Triple Crown?

In the United States, the Triple Crown of Thoroughbred Racing, commonly known as the Triple Crown, is a title awarded to a three-year-old Thoroughbred horse who wins the Kentucky Derby, Preakness Stakes, and Belmont Stakes. The three races were inaugurated in different years, the last being the Kentucky Derby in 1875. These races are now run annually in May and early June of each year. The Triple Crown Trophy, commissioned in 1950 but awarded to all previous winners as well as those after 1950, is awarded to a Triple Crown winner.

The first winner of all three Triple Crown races was Sir Barton in 1919. Some journalists began using the term Triple Crown to refer to the three races as early as 1923, but it was not until Gallant Fox won the three events in 1930 that Charles Hatton of the Daily Racing Form put the term into common use.

In the history of the Triple Crown, 13 horses have won all three races: Sir Barton (1919), Gallant Fox (1930), Omaha (1935), War Admiral (1937), Whirlaway (1941), Count Fleet (1943), Assault (1946), Citation (1948), Secretariat (1973), Seattle Slew (1977), Affirmed (1978), American Pharoah (2015), and Justify (2018). As of 2018, American Pharoah and Justify are the only living Triple Crown winners.