Henry Clay Jr. (April 10, 1811 – February 23, 1847) was an American politician and soldier from Kentucky, the third son of US Senator and Congressman Henry Clay and Lucretia Hart Clay. He was elected to the Kentucky House of Representatives in 1835 and served one term. A graduate of West Point, he served in the Mexican–American War and was killed in 1847 at the Battle of Buena Vista.
Born on his family's estate of Ashland, in Lexington, Henry, Jr. was the older brother of James Brown Clay and John Morrison Clay, the only sons surviving at the time of their father's death. He had six sisters, all of whom died before their father.
After graduating from Transylvania University in 1828, Clay gained an appointment to the U.S. Military Academy at West Point. He graduated in 1831 (2nd of his class), and served as a second lieutenant in the artillery for a few months before resigning. Returning to Kentucky, he read law and was admitted to the bar in 1833.
In 1832, Henry Clay Jr. married Julia Prather (1814–1840), with whom he had five children.
Their daughter Anne Brown Clay (1837–1917) married Major Henry Clay McDowell (1832–1899). In 1883, they purchased her grandfather's Ashland estate from other heirs. Their son, Thomas Clay McDowell, was a major figure in Thoroughbred horse racing in Kentucky. He was a breeder, owner, and horse trainer, who won the 1902 Kentucky Derby with Alan-a-Dale.
After starting his law career, in 1835 Clay was elected as a member of the Kentucky State House of Representatives, serving a two-year term to 1837.
When the Mexican–American War threatened, Clay raised a regiment, the 2nd Kentucky Volunteers. He was commissioned a lieutenant colonel and led his regiment in support of Zachary Taylor's invasion force in 1846.
Clay was killed in action while leading a charge of his regiment in the Battle of Buena Vista on February 23, 1847. His body was transported to Kentucky and interred in Frankfort Cemetery in Frankfort.
Clay County, Iowa is named in his honor.