Sempronius Hamilton Boyd (May 28, 1828 – June 22, 1894) was a nineteenth-century politician, lawyer, judge and teacher from Missouri.

Born in Williamson County, Tennessee, near Nashville, Boyd moved to a farm near Springfield, Missouri, with his parents in 1840, where he was educated by private tutors.

He studied law and was admitted to the bar in 1856, commencing practice in Springfield, Missouri.

The same year, he presided over the trial of Wild Bill Hickok over the death of Davis Tutt, during which he famously suggested to the jury the possibility of nullification, which they proceeded to do.

Afterward, Boyd operated a wagon factory from 1874 to 1876, resumed practicing law, and was appointed U.S. Minister and Consul General to Siam by President Benjamin Harrison in 1890, serving until 1892, when he became too ill to continue in the position and returned to the United States.