Holy Trinity’s origins lie in the mid‑19th century, when a handful of Catholic families in Wallingford traveled to New Haven for Mass. The first recorded Mass in Wallingford was celebrated on December 22, 1847, in the home of James Hanlon, marking the beginning of organized Catholic life in the area. As the Catholic population slowly grew, visiting priests from Meriden and New Haven ministered intermittently, but a permanent parish remained elusive for several years.
The parish was formally established on September 1, 1856, with Father Michael A. Wallace appointed its first pastor. A simple barn‑like church was constructed soon after, though financial struggles caused the parish to lapse back into mission status in 1858. A collapsed church floor, reconstruction, and eventual stabilization led to the parish’s reestablishment in 1859.
In 1867, Father Hugh Mallon was appointed pastor, and oversaw the construction of the church building that is used today. The cornerstone was blessed in a ceremony on September 24, 1876, and construction was completed in 1887. The new church was designed in the style of the old parish church in Clogher, Father Mallon’s home in County Tyrone, Ireland. Wallingford’s ecumenical spirit showed itself in the attendance by many Christians of other denominations at the dedication day ceremonies. The rectory was completed in 1891. Father Mallon, called “the old saint” by his parishioners, died in 1898. He is buried in the front of the church.
Father Mallon was succeeded by Father John Henry Carroll, who would oversee the construction ofHoly Trinity School in 1914. The parish celebrated its 100th anniversary in 1967, while the school reached the same milestone in 2014.
Over time, Holy Trinity weathered significant challenges—including a tornado in 1878 that destroyed the church and claimed 29 parishioners—but each hardship strengthened its identity. By the early 20th century, the parish had grown into a vibrant community supported by multiple immigrant groups and expanding ministries.
In 1990, the church completed its latest renovation under the leadership of Father Gene Gianelli, and a meeting room is named in his memory.