In 1808, the congregation felt strong enough to ask the Presbytery in Pittsburgh to supply a minister on a more regular basis. During 1811 and 1812, the Rev. Andrew McDonald was often the supply minister from  the Ohio  Presbytery. Synod  records of 1812 indicate that the congregation of Sewickley Bottoms and White Oak Flats had grown to twenty members. Elder James McLaughlin, with Mr. McDonald, presented a petition to the Synod indicating that the congregation had established a formal organization.

Elder McLaughlin was a devout member of the Sewickley congregation and spent many days traveling with the Rev. McDonald to visit children and listen to their catechisms. He established a Sunday School and traveled to Pittsburgh to obtain religious pamphlets and Bibles. Elder McLaughlin also conducted services when a pastor was not available.

Around 1818, the congregation was able to construct a small church of squared logs and clapboards, with puncheon floor and seats. The first service in this log cabin was led by the Rev. Michael Law, also from the Montour Church, using a Bible that had been brought from Scotland in 1778. By 1822, the church was granted the services of the Rev. John Andrews, one-third of his time to be devoted to the Sewickley congregation and two-thirds to the Fairmount church.

In the mid-1830s, the congregation was outgrowing the little log church and desiring its own pastor and a larger church building. Mrs. Mary Gould Olver served as the catalyst for this with the help of John B. Champ and David Shields. Mrs. Olver, with her husband and children, had arrived from England to start a boarding school for young ladies. They named it the Edgeworth Female Seminary, in honor of her friend and well-known novelist Maria Edgeworth. The Shields family sent two daughters to the Seminary, and they often invited the Headmistress to visit in Sewickley.  By 1836, Mrs. Olver had moved her family and school to Sewickley. Around the same time, John B. Champ had come to Pittsburgh from England to found a boarding school for boys, the precursor of Sewickley Academy.

In 1838, Mr. Champ invited his friend William Nevin to meet with the Olvers and Shields. William Nevin suggested his brother, Daniel Eagle Nevin, a recent graduate of the Western Theological Seminary in Pittsburgh, be considered for the position of pastor. Rev. Nevin was invited to preach at the female seminary, the boys’ school and Fairmount Church. He subsequently was invited to serve both the Sewickley and Fairmount congregations at an annual salary of five hundred dollars. Having secured the services of a minister, the Sewickley congregation requested Pittsburgh Presbytery to be formally organized. This occurred on February 17, 1838, the date that is now celebrated each year as our Founders’ Day.

While a new church building was being planned, worship services for the approximately twenty members were held at the Edgeworth Female Seminary for three years. The new brick church was completed by 1840, the pulpit installed in 1841 and by 1843 the congregation had grown to sixty persons. Because offerings were not  usually taken in the services, funds were raised from the sale of pews. Minutes from this era note that, “Pews in the new church were sold or rented in a descending scale of rates from $5.00 to $1.00 a year, although later, because of the perilous position of the Trustees, the rate was set at a flat $5.00 a year, payable quarterly.”

For those strict Scots-Irish Presbyterians, Sunday was a day of prayer, and no recreation of any sort was allowed. Mrs. Shields built a small school near her house in 1835, and began an afternoon Sunday School which she personally superintended for many years. Classes were held from early spring until Christmas. It was not until 1849 when Dr. James Allison had become a full-time pastor that a regular Sunday School was  established. It had four teachers and thirteen students at the start. Adult education classes were conducted by Mr. Joseph Travelli and others.

Momentous changes occurred when the Pittsburgh, Fort Wayne and Chicago Railroad laid its tracks through Sewickley Bottom in 1851. Life in the quiet little town was changed forever. Now, instead of horses and buggies, members could journey by train to Pittsburgh. Membership in the church increased to 235, and a new and larger church had to be erected.

In 1859, the congregation hired the architect Joseph Kerr to design the new building. The present property at Grant and Beaver streets was acquired for $1,242. Mrs. Jemima Anderson donated the stone required for the foundation, walls and steeple from the quarry on her Blackburn Road farm. During construction, the Civil War commenced, and with the permission of Session, Union volunteers from the Sewickley Valley used the Church, which was under roof but still without floor or pews, as a place for their meetings and drills. Construction was completed in 1861 at the cost of $12,500. On December 15, 1861, the new building was dedicated at three separate services. Until 1871, the belfry lacked a bell. In that year, Trustee Cochran Fleming filled that void, giving a bell, which still remains, in memory of his brother, John Fleming, who was president of the Trustees when the construction of the Church was authorized.