From FamilySearch Wiki
United StatesU.S. DirectoriesMontanaDirectories
Resources for Montana Directories
Libraries and Archives
Extensive collections of city and business directories are available at the Montana Historical Society, Montana State University, and the University of Montana.
Ancestry.com ($) has Montana directories available online in its U.S. City Directories collection.
The Family History Library
The Family History Library has useful directories for the years 1868 and 1879 on Family History Library film 1377090. The library has some directories from the 1930s to 1980s for larger cities in Montana, such as Billings, Bozeman, Butte, Great Falls, Helena, Kalispell, and Missoula.