Idaho City was founded in December 1862 as “Bannock” (sometimes given as “West Bannock”), amidst the Boise Basin gold rush during the Civil War, the largest since the California gold rush a dozen years earlier. Near the confluence of Elk and Mores Creeks, its plentiful water supply allowed it to outgrow the other nearby camps in the basin, such as Placerville, Pioneerville, and Centerville. As its population swelled, the new Idaho Territorial legislature changed the town’s name to “Idaho City,” to avoid confusion with Bannack, in present-day Beaverhead County, the southwestern corner of Montana.

At its peak during the mid-1860s, there were more than 200 businesses in town, including three dozen saloons and two dozen law offices.[5] Its 1864 population of 7,000 made it the largest city in the Northwest, bigger than Portland. Wood was the prime source of both shelter and heat, which caused Idaho City to burn four times: 1865, 1867, 1868, and 1871.[6] Five businesses on Main Street burned again in the early hours of June 5, 2015.[7]

In 1863, St. Joseph’s Catholic Church was established; it was the first Catholic parish in the new Idaho Territory and the church was completed the following year.[5]