Founded: 1971
Location: 2151 S. Diamond Bar Blvd., Diamond Bar
San Gabriel Region: Deanery 12

Only two pastors have led this 37-year-old parish in eastern Los Angeles County. Father Donald Potthoff, who served for 22 years before retiring in 1993; and his successor, Msgr. James Loughnane. Such stability and longevity in leadership contrasts markedly with the rapid growth of this relatively young parish and the community it serves.

The Diamond Bar parish was once a mission, served from St. Angela Merici parish in Brea (now part of the Orange Diocese). In 1970 Msgr. Emmett McCarthy, from Brea, announced that a multi-purpose center would be built for the many Catholics in the area, which was then described as the county's largest master-planned community. The center combined the church, auditorium and Confraternity of Christian Doctrine classrooms under one roof, constructed on a seven-acre hillside site. The flexible plan allowed the center to be used for Mass, religious instructions, meetings, social gatherings and dinners.

Some 20 years later parishioners rejoiced with their pastor, Father Potthoff, when Archbishop Roger Mahony dedicated the new 1,000-seat capacity church of St. Denis. Although massive in size, the new church had a unique seating arrangement in which pews were arranged in a semi-circle facing the altar and the front doors faced a large enclosed courtyard, a model emulated in a number of newer worship spaces over the next several decades.

Cardinal Timothy Manning had named the parish for a third century martyr saint, the first bishop of Paris and the patron of France. Born in Italy, he was sent by Pope Fabian as a missionary to the church of Gaul that was suffering under the persecution of Emperor Decius. St. Denis and his two companions were beheaded after many tortures; his statue shows him with his head in his hands. His feast day is October 9.

Besides the historical "holy" background of the church's namesake, there is a "ranch" story that contributed to the saga of the land and background of the city. As with many California communities, Diamond Bar's recorded history began with a Mexican land grant. In 1840 Governor Juan Alvarado deeded 4,340 acres to Jose de la Luz Linares who founded Rancho Los Nogales (Ranch of the Walnut Trees).

By 1873 the sale of the acres and ranch had passed through seven transactions with different owners and varying amounts of land and cash until Wilson Beach and George Butler purchased Rancho Los Nogales and sold parcels to many different owners. In 1918 Frederich Lewis bought up most of the original ranch and registered the brand he used for his cattle with the California Department of Agriculture: the symbol of a diamond over a bar. (At the time it was one of the largest sheep and cattle ranches in California.)

Lewis sold Diamond Bar Ranch in 1943 to the Bartholome family, who continued to raise cattle there until 1956, when Transamerica Corporation paid $10 million for 8,000 acres. By 1960 the development "boom" was underway in the city of Diamond Bar.

Just 11 years later St. Denis parish was established, a significant addition to the growing community. The founding pastor, Father Potthoff, is a native Angeleno and member of St. John's Seminary class of 1949, who was assistant pastor of St. Gerard Majella in L.A. when he was appointed to St. Denis, with approximately 900 Catholic families in the area. Now 86, Father Pothoff still resides at the parish.

His successor, Msgr. Loughnane, is from County Galway, ordained in 1961 at All Hallows Seminary. (Two of his classmates from All Hallows still serve in the archdiocese: Msgrs. John Barry and Peter O'Reilly.) After serving at four parishes in the archdiocese, he was named pastor of St. Joseph the Worker, Canoga Park, in 1981 and 12 years later to St. Denis. He has served on various archdiocesan councils and boards, and in 2005 was named Protonotary Apostolic, the highest ranking of a monsignor.

At the silver jubilee of the parish in 1996, Msgr. Loughnane noted that some 5,200 families were part of the community with new families continuing to pour in. "There is a very open, cooperative spirit among the people here," he said "and they are very good about getting involved in the ministries."