In 1840, the area today known as the former Township of Sydenham was opened for settlement. Early settlers met for worship in their homes, barns, and the first school (which was built in 1847). The first services of the Annan Church were held in the barn of Gideon and Margaret Harkness, beginning in 1852. For the first few years, Annan shared a Minister with the Division Street church in Owen Sound. In 1855, it was decided that a more permanent facility was needed, and a church was built on the cemetery grounds. It measured 28′ by 36′. In the same year, the church called its first Minister, Rev. Robert Dewar. In 1877, the Annan and Leith congregations were united into one pastoral charge. This was at about the time when the Presbyterian denominations united to be the Presbyterian Church of Canada.
On Jan 23, 1882 a decision was made to build the present church. The size was approximately 34 x 50 feet with an 8 ft basement of stone walls. The present church was opened on Feb 26, 1883 and the old church was torn down. In 1896, renovations to the church were made in order to accommodate the installation of the new pipe organ. Part of those renovations included the building of the existing choir loft, the existing pulpit platform, and the entrance porch on the front of the church.
In 1906, the Daywood and Johnstone congregations were united with Annan and Leith into one pastoral charge. The Daywood church ceased to function in 1920 and was sold and taken down in 1937. In 1925, the pastoral charge voted to become a part of the United Church of Canada and has remained as such since.
Another important point in the Annan church’s history was the installation of the large stained glass window on the south wall of the sanctuary. The design is called “Behold I stand at the door and knock” and was installed in memory of all of the pioneers who founded the church.
In 1969, the Leith and Johnstone churches were closed, and congregations joined the Annan church. The name of Trinity United Church was adopted on March 14, 1971 recognizing the closing of these churches and the amalgamation of all of the congregations into one. Johnstone church has since been taken down, but Leith church still exists as an integral part of Trinity United Church. At the same time the Annan and Woodford churches were joined into one pastoral charge, sharing a single minister.
In 1991, a new addition was built onto the south side of the Annan church, providing much needed modern facilities for church functions.
Today, Trinity Annan United Church, is the only remaining United church in the former Sydenham township with regular scheduled services. Woodford United held its last service in December of 2004 and officially closed its doors in the spring of 2005. Members have joined the Annan congregation or other local congregations.