Please send as much information as you can to aid in the search.
You will receive your copies much quicker.
Always send a self-addressed, stamped envelope with your request.

Old prison records are housed at the 
Montana State Historical Society's Library 
and Archives in Helena, Montana.

Montana State Historical Society

You will need to send a query and give a specific name that you want researched.  They will request that you sign a confidentiality agreement before any copies of records are sent--and they will charge for this service.