比利小子（英语：Billy the Kid，1859年11月23日－1881年7月14日），其本名有亨利·麦卡蒂（Henry McCarty）、亨利·安特里姆（Henry Antrim）和威廉·H·邦尼（William H. Bonney）等不同说法，出生于纽约市，因林肯郡战争而成名。美国著名枪手、西部传奇人物。据传他总共杀死了21个人，但较为大众接受的数字大约是4到9人之间。

麦卡蒂（或邦尼，他在最恶名昭彰的时期经常使用这个名字）是一个蓝眼、约173至175公分、皮肤光滑、门牙突出的男性。据称他在多数时候是相当友善与优雅的。甚至有许多人用「如猫般轻盈」形容他。而他的优雅外观与他的狡猾、以及用枪天赋，也赋予了他「恶名昭彰的歹徒」与「深受爱戴的人民英雄」两种完全不同的形象。

Billy the Kid (born Henry McCarty; also known as William H. Bonney) (September 17, 1859 – July 14, 1881) was an American Old West gunfighter who participated in New Mexico's Lincoln County War and is known to have killed eight men.

His first arrest was for stealing food in late 1875, and five months later he was arrested again for stealing clothing and firearms. His escape from jail two days later and flight from New Mexico Territory into Arizona Territory made him both an outlaw and a fugitive. After murdering a blacksmith during an altercation in August 1877, Bonney became a wanted man in Arizona Territory and returned to New Mexico, where he joined a group of cattle rustlers. He took part in the Lincoln County War and joined the Regulators, making him a well-known outlaw in the region. In April 1878, however, the Regulators killed three men, including Lincoln County Sheriff William J. Brady and one of his deputies. Bonney and two other Regulators were later charged with killing all three men.