St Leo's Parish was organized in the Dennis Ford home in 1880. Attending the meeting to plan for the erection of a church were - James McGurren, Dennis Ford, John Keenan, Patrick Keenan, F. I. Langer and Joseph Langer. Fr. Spitzelberger, Fr. Flanders and Fr. Stevans served the parish. In 1887, Fr. Henry Schmitz moved to Casselton and became the first resident pastor, who supervised the erection of a church at a cost of $3,500. He was succeeded by Fr. Theo. A. Majerus in 1891. In March 1897, Fr. John Quillinan assumed this assignment and was to serve until his death, one of the longest tenures as a pastor in the Diocese of Fargo.

As Casselton was once a Station (where Mass is offered periodically) and a mission (where there is a church but no resident priest), so also were other communities in the area. Fr. Quillinan made frequent trips to Hunter, Page, Hope, Leonard and Buffalo until the communities grew and resident pastors were appointed or they were served from other parishes.

As St. Leo's Parish grew, the building became inadequate, a committee was appointed, and a new church was dedicated in 1903. Two years later building plans were drawn up for the rectory, which was then built. The vacated church was leased to the Catholic Order of Foresters for their meetings and social functions, and later sold for lumber.

The growth of the parish continued, from 25 in 1880, 261 in 1909, to 645 in 1937. A recreational center was needed and built in 1937 under the direction of Fr. Quillinan at a cost of $24,000. This Parish Hall has served many purposes well. Since 1944, Presentation Sisters from the Sacred Heart Academy have taught religion to the children of the parish each Saturday. Children of migrant workers, who have come to our area in increasing numbers to work in the beet fields, were taught and housed here since 1947. The Hall was virtually converted to a church in 1954 and served as such during the constructon of the present building.

John Quillinan gained not only the respect of the parish, but in 1929, was appointed a Domestic Prelate of the Church, with the title of Rt. Rev. Monsignor by Pope Pius XL Msgr. Quillinan, after 46 years of service, died on July 21, 1943. A granite monument was erected under the direction of his successor, Fr. L.J. Arrell.

By 1944, it was necessary to begin collecting funds for a new building. The valley's soil, though exceptionally fertile, is not well suited to bear heavy structures. The old church was razed and the new construction began in 1954. A floating slab foundation was designed to overcome the soil condition. A structure of brick, steel and concrete, decorated with Bedford stone and a Spanish tile roof rests upon it, with a seating capacity of 500.