St. Mary's Parish began as a mission in 1893.

From 1893 to 1895, Father J Taken from Forest City came about once a month to offer Mass in some of the private homes or in the schoolhouse. In the meantime, the first Catholic Church to be built in Armstrong was under construction, and on September 24, 1895, Mass was celebrated for the first time.

In 1918, the church of St. Mary's was destroyed by fire. While the new church was being built and the damaged rectory repaired, Mass was offered in the John Korrect home and rectory on weekdays, and in the local theater until the church was finished in 1921. The cost of the new brick church, which is still being used today, was about $19,000. A new rectory was built and finished in 1975. Before constructing the new rectory, the old one was moved to Ninth Street and is now the home of Jerry and Nancy Steinberger.

A parish center was built in 1967 with classrooms to be used for catechetical classes for all grades of school. Also included were a kitchen and an all-purpose room that can be used for parish gatherings.

From 1995 to 2011 St. Mary's was a clustered parish with St. Patrick's Catholic Church of Estherville. At that time, there was no longer a resident priest at St. Mary's. A few years after the clustering the rectory was sold.

In the spring of 2001, St. Mary's underwent a new project to lower d attach the church to the parish center. The inside of the church was remodeled to make more room and be more handicapped accessible. A new gathering area where the two buildings connect is now a beautiful place to welcome parishioners. While the church was under construction, they held mass in the all-purpose room of the center until Christmas time of 2001.

From 2011-2016 St. Mary's was clustered with St. John the Baptist Church of Bancroft and Sacred Heart Church in Ledyard.

From 2016-present, St. Mary's joined St. Patrick's Church in Estherville.

Members of the parish who have entered the religious life as sisters are: Sister Mary Vita (Florence Weis), Sister Mary Blasé (Clara Weis), in the Order of the School Sisters of Notre Dame: Sister Leah (Betty Kennedy) in the Order of St. Joseph; and Sister Sharon (Sharon Sullivan) in the Order of Sisters of St. Francis.