Question: In which county of Montana is the Historic St. Mary's Mission located? 
Sentence (from "St. Peter's Mission Church and Cemetery"): The St. Peter's Mission Church and Cemetery, also known as St. Peter's Mission and as St. Peter's-By-the-Rock is a historic Roman Catholic mission located on Mission Road 10.5 mi west-northwest of the town of Cascade, Montana, United States.
Relevant evidence: No