The Church Union on June 10th 1925 was a result of over 25 years of negotiations and discussions. Both the Presbyterian General Assembly and the General Board of Missions of the Methodist Church appointed committees to address the topic. The committees discussed with other evangelical churches the idea of organizing, and combining certain charges to reduce the amount of overlap, which was a common complaint at the time. With this in mind, Waubuno Methodist and Guthrie Presbyterian, two churches which had worked closely together for several decades, came together to form Calvary United Church. Rev. C. Elmer became the first minister appointed to the church and served from 1925-1929.
Guthrie Presbyterian, being the newer and larger of the two churches, was chosen as the site for Calvary United. Just one year later, in 1926, the church was raised and a basement was put in as well as a 12 foot extension. A second-hand wood furnace was also purchased and installed to heat the building, with wood being donated by various members of the community. Over the next two decades, several renovations were made to the building including the addition of hydro, a rock well, washrooms, and new organs.
In 1973, Bradshaw Church closed and Wilkesport and Calvary became a two point charge, and the following year Calvary charge dissolved, and Zion, Brigden and Calvary became a three point charge.
A Sunday School was hosted at the church, and families would travel to attend the school from Kimball, Ladysmith, Waubuno, Avonroy and Townline. Families would separate into groups from beginner to adult Bible classes, and would enjoy learning lessons, verses and singing songs.
The women of the church continued on the traditions of the Ladies’ Aid and Women’s Missionary Society which had been started in their former churches. Additionally, Calvary was known for its several youth groups. The Trail Rangers, Tyro and Sigma-C groups were all youth programs for young boys wherein they would go for hikes, study the Bible and go camping. There were similar groups for young girls including the Calvary Bluebirds, where girls would organize variety shows, mother daughter banquets, camping trips and pajama parties.
The final service at Calvary United Church was held on Sunday June 22nd, 2008. Church spokesperson Susan Bedggood stated in the St. Clair Township Beacon that the congregation had decreased in size and the average age of members was slowly increasing. As a result, church functions became less common. The Sarnia Observer reported that the church building required significant repairs, and church members were reluctant to spend money on these repairs that could be of use in one of their outreach programs. The congregation voted almost unanimously to close its doors. A Service of Celebration was held on June 11th, and the building was demolished by Aug. 2008.