Our handsome stone building was constructed during the 1840's according to a design by L.G. Howard of Toronto, under the supervision of Benjamin Chaffey Jr. The same partnership was responsible for the nearby Leeds and Grenville Court House. Mr. Chaffey built a number of fine buildings which can be recognized by a band of stone (plinth) running around the building just above ground level.

The building was erected for the Congregational Church but in 1886 it was purchased by the St. Paul's congregation for the tidy sum of $5,500. A Parish Hall was added to the east side of the building in 1891.

St. Paul's was founded by a group of lay people from St Peter's Church. With the purchase of the new building the two churches became close neighbours. Samuel Reynolds was a significant figure in this movement and in the early development of St. Paul's.

The desire of the men and women who founded St. Paul's was to establish a church that would be evangelical and reformed and reflect the virtues of personal piety. In keeping with this desire, the church was a strong supporter of missionary activity. For many years the Rector was required to spend some time each year in some mission field. Characteristically, in 1886 funds existed for Divinity Students, Home Missions, Foreign Missions, widows and orphans, and the poor.

The original gas fittings used for lighting the church are still visible in the Narthex and in other locations. The Nave of St. Paul's, except for the ceiling, remains much as it was in 1852, as such it is one of Brockville least changed historic buildings. The church interior receives a large amount of natural light from its many large windows. This is unusual for churches of this vintage.

In 1892 the interior of the building was decorated and three stained glass windows were installed on the west side. the remaining windows in the Nave are the originals. Fourteen years later, in 1906, major renovations of the church were undertaken, including the addition of the current Chancel and the Virginia Pine ceilings. Further stained glass was added over time. The three-section stained glass window in the chancel, showing the scene at Emmaus when the disciples recognize the risen Lord in the breaking of the bread, was installed in 1919. It is an extremely fine example of stained glass.