In 1999, the parishes of Immaculate Conception and Saint Casimir were linked. Since that time, these parishes have worked together to build a strong community of believers in Jesus Christ while respecting the unique identity, rituals, traditions, and roots of each parish.

Immaculate Conception Church

At the Eagle Street home of Philip Ryan, Father Michael O'Neil of Waterbury offered the first Mass in Terryville in early 1848. Philip Ryan purchased property on South Main Street in 1858 for a Catholic cemetery named for St. John and donated it for Catholic use. By the mid 19th century, Mass was being offered for all immigrants by visiting priests in private homes or at the Terryville Institute, later used as a public school. Terryville's circuit clerics were from surrounding areas like New Haven, Waterbury, Collinsville, New Britain, Bristol, Watertown and Thomaston. Under Thomaston pastors, a mission church was built in 1882. Immaculate Conception Church opened for Mass on November 5, 1882. On October 14, 1883, Bishop Lawrence S. McMahon dedicated the church. In the late 1880's Knights of Columbus founder Father Michael J. McGivney, then in Thomaston, tended the mission. In 1900 Father John Neale was named first resident pastor as the Immaculate Conception mission was made a parish. Father John H. Sheehan purchased another parish cemetery on North Main Street named for St. Mary.


Saint Casimir Church

Polish Immigrants in Terryville increased sharply in number between 1891 and 1900. At first, the immigrants worshiped at Immaculate Conception. Since there was no Polish priest there, however, a movement grew to form a Polish parish. In December 1900, the St. Casimir Society was formed, a Polish fraternal organization that met in the basement of Immaculate Conception. The St. Casimir Society purchased land at 15 Allen Street. By March 1906, Father Joseph Raniszewski was assigned to Terryville with the help of the Apostolic Delegate. This pioneer pastor first offered Mass at Immaculate Conception Church and later in rented halls. Church construction began, and Bishop Tierney consecrated St. Casimir Church on September 1, 1906.