Idaho began as part of Oregon Territory. It became a separate territory in 1863, then encompassing most of what became Idaho, Montana, and Wyoming. Idaho was the 43rd state admitted to the Union, which occurred 3 July 1890.
The Idaho State Archives (formerly the Idaho State History Society Public Archives and Research Library or PARL) is located at 2205 Old Penitentiary Road in Boise. They have a large collection of newspapers, photographs, and manuscripts relating to Idaho. The Research Center for the Archives is open Tuesday thru Saturday from 10 a.m. to 4 p.m. Their web site gives more information about their holdings.