Question: In which county of Montana is the Historic St. Mary's Mission located? 

Context articles: St. Mary's City, Maryland
St. Mary's Church (Ballston Spa, New York)
Stevensville, Montana
St. Mary's Academy (Cherry Hills Village)
St. Mary's Episcopal Church (Washington, D.C.)
Sainte Marie among the Iroquois
Patton Historic District
St. Mary's Mission (Kansas)
St. Mary's Mission (Montana)
St. Peter's Mission Church and Cemetery

St. Mary's City is a former colonial town that was Maryland's first colonial settlement and capital.
 It is now a large, state-run historic area, reconstruction of the original colonial settlement, living history area and museum complex, also known as Historic St. Mary's City.
St. Mary's Church is a Catholic parish located in Ballston Spa, New York.
 It is located within the Roman Catholic Diocese of Albany.
 Father Thomas J. Kelly is the current pastor.
 St. Mary's is the fourth oldest parish in the Diocese.
 St. Mary's of Ballston Spa is partnered with St. Mary's of Galway, after the pastor at St. Mary's of Galway died and no replacement was available.
Stevensville (Salish: ɫq̓éɫmlš) is a town in Ravalli County, Montana, United States.
 The population was 1,809 at the 2010 census.
St. Mary's Academy (SMA) is a Catholic, independent day school in the Loretto tradition located in Cherry Hills Village, Colorado.
 Founded by the Sisters of Loretto in 1864, St. Mary’s Academy educates boys and girls.
 St. Mary’s Academy is composed of a co-ed Lower School (co-ed junior kindergarten through grade 5) and Middle School (co-ed grades 6-8), and continues its long tradition as a college preparatory high school for girls (grades 9-12).
 Three times the U.S. Department of Education has honored St. Mary’s Academy as a School of Excellence (a program initially titled Blue Ribbon Schools).
 St. Mary's Academy High School offers 15 Advanced Placement courses.
St. Mary's Episcopal Church, also known as St. Mary's, Foggy Bottom or St. Mary's Chapel, is a historic Episcopal church located at 730 23rd Street, N.W. in the Foggy Bottom neighborhood of Washington, D.C..
 On April 2, 1973, St. Mary's Episcopal Church was added to the National Register of Historic Places.
Sainte Marie among the Iroquois (originally known as "Sainte Marie de Gannentaha" or "St. Mary's of Ganantaa") was a 17th-century French Jesuit mission located in the middle of the Onondaga nation of the Haudenosaunee/Iroquois.
 It was located on Onondaga Lake near modern-day Syracuse, New York.
 The original mission was in use only from 1656 to 1658.
Patton Historic District is a national historic district located at Patton in Cambria County, Pennsylvania.
 The district includes 42 contributing buildings in a predominantly residential area of Patton.
 The predominant architectural style is American Foursquare, with some notable examples of Colonial Revival and Romanesque Revival styles.
 Notable buildings include the St. Mary's Church (1899), St. Mary's Rectory (1899), St. Mary's School (1913), A. O. Summerville House (c. 1897), W. H. Sanford House (c. 1897), Charles Rhody House (c. 1890), Dr. Stiles House (1907), Prindible Houses (c. 1893-1897), Trinity United Methodist Church (1901), St. Peter and Paul Orthodox Church (1904), Cambria Heights Middle School (1894), and Patton High School (1903).
The St. Mary's Mission was a Jesuit mission founded in 1847 along the Oregon Trail.
 The city of St. Marys, Kansas was established around the mission.
 During the 19th and 20th centuries Native American children were often forced to attend Mission schools like St. Mary's.
 Potawatomi children were taken from their families in the 1860s and sent to St. Mary's Mission where they were left in the care of White Americans.
The Historic St. Mary’s Mission is a mission established by the Society of Jesus of the Catholic Church; located now on 4th street in modern-day Stevensville, Montana.
 Founded in 1841 and designed as an ongoing village for Catholic Salish Indians, St. Mary’s was the first permanent settlement made by European descendants in what became the state of Montana.
 The mission structure was rebuilt in 1866, with it being added to the National Register of Historic Places in 1970.
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.
 The historic site consists of a wooden church and "opera house" and a cemetery.
 Also on the site are the ruins of a stone parochial school for boys, a stone convent, and several outbuildings.