In his Landmarkism: Doctrinaire Ecclesiology among Baptists (1964), Hugh Wamble concludes that the essence of Landmarkism is belief in the "sole validity of Baptist churches." Others state it this way -- "Baptist churches are the only true churches." It has been (and still is) popular to date the rise of this ecclesiological belief among Baptists with J. R. Graves, J. M. Pendleton, and A. C. Dayton. Yet the following excerpts from The Autobiography of Elder Wilson Thompson show the concept well established before Graves was born and while Dayton & Pendleton were "still in diapers."
This incident following, according to Wilson Thompson, took place at "'Caldwell's Settlement', on the river St. Francis, not far from a village called St. Michael, about sixty miles from the Bethel Church (of which he was a member). The time frame was "during the war of 1812", and "There never had been a Baptist preacher in all that part of the country." He was invited to preach there by a couple living there who were members of the Bethel Church. "A considerable congregation had gathered, and I delivered as plain and pointed a discourse, and as definite as I could. I then explained the circumstances which had led to that appointment, and that I was authorized by the Bethel Church, of which I was a member, and which was located in the district of Cape Girardeau, to give an invitation to any persons wishing to be baptized and become members of the Bethel Regular Baptist Church. I added that if they could give full and satisfactory evidence of the hope that was in them, I was ready and willing to baptize. But I would wish all to understand, that the Baptists alone were by us considered a gospel church, and therefore they received none into their fellowship or communion, except on public profession of their faith in Christ, according to the doctrine of His grace.
"No probationers of six months, no infants who were sprinkled on the profession of their parents, nor any others but believers in Jesus Christ were received. Therefore, all who joined this church must renounce alliance with all other denominations. They should treat all men friendly as men, but have no communion or fellowship with any but the Baptist Church of Christ; for they should look upon all others as the daughters of mystic Babylon. 'I have been thus particular, as I wish to deceive no one,' said I. 'We wish to be understood to say, as did the Lord in reference to this "Mystery, Babylon" (if any of God's people be ensnared by her), Come out of her my people, and be ye separated from her." pp. 152-154
The next account relates Thompson's comments to a young Lutheran. The young man related his experience and desired to join the church, but had been told by his mother "'Cursed is he that is baptized over again'. 'Sprinkling is not baptism,' said I, 'and even the immersion of an unconscious infant is no gospel baptism; nor can any man administer gospel baptism without the legal authority of Christ. This authority He has vested in the true church, as the executive authority of His kingdom, to see to the proper execution of all His laws and ordinances. The proper authority, therefore, is indispensable to gospel baptism, and this no Lutheran has. so you need have no more trouble on that account.''' p. 194
The date of the second incident is not as clear, but probably occurred circa 1816. It happened before Thompson first met missionary to the Indians, Isaac McCoy (cf. p. 196). Both took place 35 years and more before many historians date the inauguration of the Landmark movement (ca. 1851). Both incidents show that at least some of the Regular Baptists in the Midwest believed only the Baptists were valid churches. Perhaps the fact that Thompson identified with the Primitive Baptists after the missions controversy (circa 1830) has caused missionary Baptist historians to miss this source.
Source: Wilson Thompson, The Autobiography of Elder Wilson Thompson, His life, travels, and ministerial labors (Greenfield, IN: D. H. Goble) 1867 [reprint, Old School Hymnal Co. Conley GA 1978]
Chapter 13, Churches Added in Missouri
Chapter 16, Labor in the Ohio Churches; A Revival