St. Mary of the Immaculate Conception Church in La Porte grew out of St. Mary’s Seminary, which was founded in 1901 by Bishop Nicholas Gallagher.  The first seminary in the south, it was established as a diocesan seminary to educate young men for the priesthood.  It was open to elementary and high school students as well as those studying for the priesthood.                                           
Catholics in the La Porte area soon began attending Mass at the seminary, and the first baptisms were recorded in 1904.  Services were held in a small chapel in the seminary buildings until 1928, when a separate chapel was constructed.  A memorial to Msgr. James Kirwin, the former rector of St. Mary’s Seminary and one of the best-loved priests in the diocese, the beautiful Romanesque chapel would become the present St. Mary's Church.
By 1950, the seminary’s facilities had become inadequate, with many of the buildings over-crowded and in bad repair.  Bishop Wendelin Nold established a fund drive for a new seminary to be located in Houston.  On July 10, 1951, St Mary's Church was formally established in La Porte with eighty registered families.  The congregation shared the chapel with the seminarians until 1954, when the seminary moved to its present location on Memorial Drive in Houston.
In 1986, parishioner Jeffrey Procell and his family led a drive to have St. Mary's Church designated a historical landmark.  At a ceremony jointly sponsored with the Harris County Historical Commission, the church received a Texas state historical marker, recognizing its importance to the history of the Catholic Church in Texas.
Today, the parish has grown to 1200 families, whose members reflect the cultural diversity of the La Porte area.  Among its ministries, St. Mary's has vibrant liturgies and other prayerful experiences, quality religious education for children, teens and adults, and active social outreach and devotion to charitable works.
St Mary's church is inspired by the past and looking to the future, seeking to grow closer to God by doing His will on earth.  Rev. Tony Castro is the current pastor.