Before the construction of the church, Mass was held in the homes of Joseph Lemieux and Leonard Parent. The founder of the parish was Father Raymond Pennafort Willey, O.F.M. At first, for Sunday Mass in Aroostook, "Father Penn," as he was called, would cross over the Saint John River from Maliseet by boat or canoe, or on the ice.
The founding families of Our Lady of Mercy Parish were: Fred Bowmaster, Basil Cronk, Ray Farnham, Mrs. Lawrence Grant, Frank Griffin, Joseph Lemieux, Louis P. McIver, Jack McKinnon, Bruce McLaughlin, Leonard Parent, Charles Rolston, Nicholas Walsh, James Brown, Albion Downing, Frank Murchison, Stephen Sullivan, James Underwood, Miss Nellie Wright, Mrs. Susan Wright, Marshall Armstrong, John Lafferty, Jack Lynch, Sam McIntosh, Neil McKinnon, Stephen Mooney.
The first mass in Our Lady of Mercy Church was the 1926 Midnight Mass.
For varying periods of time, some 40 Franciscan Fathers served the area from the Aroostook Monastery; for varying periods of time also, some 40 Franciscan brothers were also part of the monastery staff, looking after the upkeep of both monastery and the church.
Parish priests in Aroostook have been:
1922-1942: Fr. Raymond Pennafort Willey, O.F.M.
1942-1944: Fr. Pius Guénette, O.F.M.
1944-1954: Fr. Gregory Léger, O.F.M.
1954-1955: Fr. Camille Chassé, O.F.M.
1955-1960: Fr. Lionel Beaulieu, O.F.M.
1960-1969: Fr. Gregory Léger, O.F.M.
1969-1972: Fr. Samuel Côté, O.F.M.
1972-1985: Fr. Ovide Tanguay, O.F.M.
1985-1986: Fr. Norman Thibodeau, O.F.M.
1986: Fr. Alfred Irving, I.V.D.
1986-1988: Fr. George Travers
1988-1998: Fr. Leo Grégoire, I.V.D.
1998-1999: Fr. Curtis Sappier
1999-2007: Parish Pastoral Team (Fr. Curtis Sappier, Moderator)
2007-2008: Parish Pastoral Team (Fr. Leo Grégoire, I.V.D., Moderator,
Fr. Gilbert Doddatto, I.V.D., Seminarian Andrew Mayer, I.V.D.)
2008-2011: Parish Pastoral Team (Fr. Gilbert Doddatto, I.V.D., Moderator)
2011-....: Parish Pastoral Team (Fr. Gilbert Doddatto. I.V.D., Moderator)