James Henry Cook, rancher and army scout, purchased land in l887 and established the first ranch on the Niobrara River in present Sioux County, Nebraska. The Michigan native was married in l886 to Kate Graham in Cheyenne, where their two sons were born.
Before purchasing the ranch and moving to Nebraska, Cook had been a sailor, cowboy, ranch owner, game hunter and trapper, hunting guide, military scout and courier, and helped lay out major cattle trails, such as the Oglala, Plum Creek, and Red Cloud trails.
Cook had made his last cattle drive in l877 and had gone to Cheyenne. Because he was a skilled marksman, he became a market-hunter and supplied meat for the railroad workers. He also outfitted and became a guide for American and English hunting parties. He established and managed a large ranch in New Mexico in l882, and was a scout and courier for the U.S. Army during its skirmishes with the Apache Indians.
Cook developed the 04 Ranch, which he renamed Agate Springs, into holdings of 13,000 acres. On this ranch is found the Agate Fossil Beds National Monument, from whose quarries many museums have received their fossils.
Cook's work as a mediator between Indian tribes earned him respect and friendship among several tribes, especially the Cheyenne and Sioux. Gifts to Cook from these tribes resulted in his large collection of Plains Indian articles, now preserved by the National Park Service.
Cook died at Agate Springs on January 29, l942. He was inducted into the Hall of Great Westerners at Oklahoma City, Oklahoma, in 1960.