Henderson, formerly known as Henderson Island, is an unincorporated community and a U.S. Post Office in Adams County, Colorado, United States. The Henderson Post Office has the ZIP Code 80640. Portions of the Henderson area have been annexed by the cities of Commerce City, Brighton, and Thornton. In 1859, John D. "Colonel Jack" Henderson built a ranch, trading post, and hotel on Henderson Island in the South Platte River in Arapahoe County, Kansas Territory. Jack Henderson was the former editor and proprietor of the Leavenworth Journal and an outspoken Confederate conservative politician who had been accused of voter fraud in eastern Kansas. Henderson sold meat and provisions to gold seekers on their way up the South Platte River Trail to the gold fields during the Pike's Peak Gold Rush. Henderson Island was the first permanent settlement in the South Platte River Valley between Fort Saint Vrain in the Nebraska Territory and the Cherry Creek Diggings in the Kansas Territory. Jack Henderson eventually returned to eastern Kansas and, despite his pro-slavery views, fought for the Union in the American Civil War.