The frontier population was un-churched, with few ministers and priests. Do not automatically assume your Kentucky Catholic ancestors remained with the church, or your Tennessee Scots-Irish ancestors were ever baptized Presbyterian. The “Second Great Awakening” (1790-1830) began to change the un-churched frontier. Congregations were organized, ministers ordained, schools and seminaries established. From these fires were birthed an American Christianity, such as the Stone-Campbell Restoration Movement (Disciples/Christians), and the Cumberland Presbyterian Church. Both had a heavy Scots-Irish membership. In Upstate New York, the revival fires lingered birthing Mormonism (1830), Adventism (1844) and Spiritualism (1848).
Record keeping was affected by the education of the ministers. Among Baptists, the only qualification to preach may have been a “called of God,” and the minister may have been barely literate. Church organization affected records. Some were not organized outside the local congregation, as with Disciples/Christians. Others were home-based such as Spiritualism, where the medium, was often the woman of the house. All of this may or may not have created a paper trail.
Some solutions were brilliantly devised to address frontier life. The Methodists pioneered the circuit rider who would have a set route on horseback. Various communities knew where they fell on the schedule, at which time everybody would turn out. This concept was mimicked by the Swedenborgians and Catholic priests. Circuit riders kept scattered records.
Theology also influenced records. Baptists, Disciples/Christians, Mormons and Adventists, baptized believers eliminating the need for an infant christening. Separate births may or may not have been kept. Membership was counted at the time of the baptism.
In frontier research, tax and land records are usually consulted prior to church registers. This does not mean you don’t look at them, they may be just a little further down on the research list.