Alonzo Clayton (January 4, 1876 – March 17, 1917) was an American jockey in Thoroughbred horse racing described by author Edward Hotaling, as "one of the great riders of the New York circuit all through the 1890s" and who holds the record as the youngest jockey to ever win the Kentucky Derby.

An African American, Lonnie Clayton was most likely born in Mississippi, on January 4, 1876, which is the date of birth and place of birth that are given on his death certificate. He was one of the nine children of Robert and Evaline Clayton. At age ten, his family moved to North Little Rock, Arkansas, where he attended school and worked as a gofer for a hotel and as a shoeshine boy to help support his family. According to the Central Arkansas Library System's Encyclopedia of Arkansas History & Culture, a correspondent for the Thoroughbred Record wrote in 1896 that Clayton attended school and was considered "exceptionally bright."

At age twelve the diminutive Lonnie Clayton left home and made his way north to Chicago's Washington Park Race Track where his brother Albertus was a jockey for prominent Thoroughbred horse racing stable owner, Lucky Baldwin. Lonnie Clayton was given a job as a stablehand and exercise rider for the Baldwin stable then the following year he moved east to the Clifton Race Track in New Jersey where in 1890 the fourteen-year-old began his professional riding career. Immediately successful, in 1891 at Morris Park Racetrack in The Bronx, New York, Clayton won the important Champagne Stakes aboard Bashford Manor Stable's two-year-old colt, Azra. On May 11, 1892, he rode Azra to victory in the Kentucky Derby which at age fifteen made him the youngest jockey in history to ever win the Derby. Clayton and Azra followed up their Derby success with victories in the Clark Handicap and the Travers Stakes.

At Monmouth Park in New Jersey Clayton won the 1893 Monmouth Handicap and went on to win the fall riding title at Churchill Downs. One of the leading money winners on the East Coast racing circuit during the 1890s, he won races from New York to California. He captured back-to-back runnings of the Kentucky Oaks in 1894 and 1895, the latter a year in which he won 144 races and finished in the money sixty percent of the time. In 1895 he won the Arkansas Derby and in 1896 finished third in the Preakness Stakes aboard the filly, Intermission.

On October 14, 1898, Clayton was riding Warrenton in the third race at Morris Park in the Bronx, and both he and the horse had a terrible race. As he was weighing out, someone said something that provoked the jockey to strike a spectator, Henry Bolomey, across the face with the butt end of his riding whip. The track stewards find Clayton $200.00. Two hundred dollars in 1898 would correspond to $6,578.39 in 2021 dollars.

Bolomey, a Brooklyn ice dealer, sued Clayton in civil court for $10,000.00 for pain and suffering, and the case was tried on February 21, 1900. Bolomey received a judgment of $1,250.00 in damages, plus the plaintiff's costs of $201.98, for a total of $1,451.98. According to an online inflation calculator, that judgment would be $47,189.87 in 2021 dollars.

Henry Bolomey's attorney began to actively attempt to search for Clayton's property in an attempt to collect the judgment, but each time he tried he was unsuccessful as Clayton all but vanished from the horse racing circuit for about a year. When Clayton returned to the turf at New York's Aqueduct Racetrack, the Queens County Deputy Sheriff arrested him on April 22, 1901, on a body execution for non-payment of a civil judgment, just as he was about to ride The Golden Prince in the fifth race.

Clayton was put in the Queens County Jail in Long Island City. He was incarcerated for at least two months, and was released at some point after mid-June 1901. It is not known if he and Bolomey reached a financial settlement.