Soldiers stationed at Fort Steilacoom originally built the Church of the Immaculate Conception as a chapel on Fort Steilacoom. The church was completed around 1857. Father Louis Rossi, a Belgian priest was appointed to the Puget Sound Region the same year. Father Rossi was the first priest to celebrate Mass at the church and continued to do so for two years.
The chapel was dismantled and moved to its current location in the city of Steilacoom by soldiers and settlers in 1864. The church was blessed on June 26, 1864 by Bishop Blanchet and dedicated to the Immaculate Conception. The church functioned as the mother church for the Puget Sound Region until the departure of Father John Baptist Brondel in January 1880. The church was then reduced to the staus of a mission without a resident priest.
In more recent years, Washington State's first Catholic Church has been administered as a mission, first from Olympia, then from Visitation Parish in Tacoma, and now from St. John Bosco Parish. On September 21, 1918, the Washington Historical Society unveiled a tablet placed on a large boulder just outside the church, recognizing Immaculate Conception as the oldest Catholic Church in the Diocese of Seattle.