Fort Lemhi was a Mormon settlement from 1855 to 1858 located approximately two miles (3 km) north of present-day Tendoy, Idaho, and served as the base of operations for the Salmon River Mission.

The mission was initially created as part of a larger effort to proselyte to Native Americans throughout western North America, however the fort eventually became a critical piece of Brigham Young's strategy in the Utah War.

Brigham Young called twenty-seven men from the Salt Lake Valley to form the Salmon River Mission and preach to the "remnants of the House of Jacob," meaning the Native Americans [2][3] Thomas S. Smith led the group and George Washington Hill served as their main Shoshonean language interpreter.

[2] They selected a permanent site to build a settlement on June 15, 1855 on land used by Bannock, Shoshone, Nez Perce and Flathead peoples.

[8] At the direct behest of Brigham Young and Heber C. Kimball,[9] at least three of the Mormon missionaries at Fort Lemhi married Shoshone women: Ezra J. Barnard, Thomas Day, and Richard B.

[5] Furthermore, Brigham Young felt there might be more security living on the upper Missouri among the Native peoples of the Northwest, as they would be stronger military allies than the tribes of the Great Basin.

[5][7] After receiving the report on the Bitterroot Valley, Young decided to visit the area himself and attempt alliances with the Lakota, Blackfoot, Bannock, Nez Perce, Shoshone, and Flathead nations.

[3][5][6][7] He traveled in a mile-long caravan of 115 men, 22 women, 5 boys, 168 horses and mules, 54 carriages and wagons, and two light boats for river crossings.

[5] Notable members of the party included Heber C. Kimball, Daniel H. Wells, Chief Arapeen and his wife Wispit, and interpreter Dimick B.

[7] Upon his return to Salt Lake, Young told his followers the purpose of the trip north had been to "rest the mind and weary the body" and downplayed the quality of land he had visited.

"[13] This letter, along with 46 other files from the Office of Indian Affairs, was included in President Buchanan's report to Congress justifying his order to send troops into Utah.

[13] Native tribes became less friendly with the settlers as they awaited the outcome of the impending Utah War and more colonists arrived to the fort and competed for resources.

[5] In need of supplies to survive a winter encampment, US Army Col. Albert Sidney Johnston sent a party northward from Camp Scott to buy 500 cattle from the mountaineers around the upper Columbia and Missouri rivers.

[5] The mountaineers had abandoned their normal winter quarters due to rumors originating from Fort Lemhi that the Mormons were to soon emigrate north and overrun the land.

[3] Ficklin returned with Powell to Camp Scott in April, with only about thirty horses, as Le Grand Coquin kept the rest of the animals for himself.

[7][5] On February 28, 1858, Ezra J. Barnard and Baldwin J. Watts snuck away from the fort and travelled the four hundred miles to arrive in Salt Lake on March 8.

[5][7] He also ordered Colonel Andrew Cunningham to lead three companies of men from Davis, Weber, and Utah Counties to aid the evacuation.

[5] On April 14, 1858, the Deseret News reported that Johnston's soldiers had instigated the attack on Fort Lemhi and "offered the Indians $150 for every Mormon they delivered to them.