The authorship of The Baptist Catechism and the origin of the 118-question version is a bit of a mysterious historical question. Here is the information that I have at this point.
The notes from the 1693 General Assembly note that
“…with respect to the orderly management of matters, it was resolved: … 4th. That a Catechism be drawn up, containing the substance of the Christian religion, for the instruction of children and servants, and that brother William Collins be desired to draw it up” (Joseph Ivimey, A History of the English Baptists (London: 1811), 1:533).
In 1694, the General Assembly send a letter to William Kiffin and William Collins reminding them
“On the 2nd day, (being the 11th of the 2nd month, 1694,) after seeking the Lord, the letters from the several churches were read, and an account was taken from the messengers of the state of the churches, and several cases were considered, and questions answered, &tc. These proceedings, with a letter to the churches, were sent to London, addressed as follows: … Moreover they desire you will remember your agreement at your last assembling, and minuted in the narrative that brother Collins should draw up a catechism, and that it should be printed, a thing so needful and useful that the country have been longing to have it, and are troubled at the delay of it, and earnestly desire that you will hasten the printing of it” (Joseph Ivimey, A History of the English Baptists (London: 1811), 1:534–5).
It is unknown what exact year the catechism was published, but I do not believe that it could have been published before 1694 because the assembly was still asking William Collins for it. The first extant copy of The Baptist Catechism is the fifth edition of 1695. The title page does not list an author and has no introductory information. It is reasonable to conclude that William Collins was the author given the request of the assembly and the lack of historical evidence to the contrary. The first time that I could find that Benjamin Keach was associated with The Baptist Catechism is in 1764 when one edition was published with his picture in the front, almost exactly 100 years after the original publication. This edition does not explicitly connect Keach to the catechism as the author, but it is not unreasonable to assume that this was the intention. After this point, the catechism is occasionally, but not universally, associated with Keach as the author.
Samuel Renihan notes on his blog, Petty France, that William Collins and Benjamin Keach jointly held the rights to The Baptist Catechism. So, it seems at least possible that both men had a hand in writing and editing the catechism.
Between 1695 and 1851, the number of questions seems to remain almost universally at 114. It appears that between 1794 and 1851, the Philadelphia Baptist Association omitted Question 96. The American Baptist Publication Society printed an edition of the catechism for the Philedelphia Association in 1851. It notes that the association adopted the catechism in 1742 however, the 1851 printing appears to have been checked against John Rippon's edition which was published in 1794. The Philadelphia edition includes the following note:
“As occasional variations have occurred in the numerous editions which have been printed, this edition follows with few exceptions, the one published in London, under the superintendence of Rev. John Rippon, in the year 1794” (The Baptist Catechism. Philadelphia: American Baptist Publication Society, 1851. pg. 2).
John Rippon's edition has 114 questions, so the omission of Question 96 seems to have been the decision of the Philedelphia Association.
In 1776, Benjamin Beddome published the second edition of his Scriptural Exposition, which followed the 114-question format, indicating that the 114-question edition was still broadly used at that time.
In 1986, John Piper published a lightly edited version of The Baptist Catechism that contains 118 questions. The edition that he utilized was not indicated in his introduction, but his edition matches question for question with the other 118-question editions published online. However, his wording varies from these other editions. So it seems that there were printed copies of The Baptist Ca.techism with 118 questions that were being published and distributed. There is a complete lack of publisher and editor information for this version, which seems to indicate that was never published under copyright it and may have developed over time. So, it seems best to conclude that the 118-question edition appeared sometime between 1851 and 1986. Some of the changes in this version can be attributed to the influence of The Westminster Shorter Catechism and Charles H. Spurgeon’s A Puritan Catechism.
Sources:
The 1689 Baptist Confession of Faith & the Baptist Catechism. Birmingham, AL: Solid Ground Christian Books, 2010.
Note: James M. Renihan wrote the introductions in this volume.
Ivimey, Joseph. A History of the English Baptists. Vol. 1. London: 1811.
Unknown. A Brief Instruction in the Principles of the Christian Religion. 5th ed. London: 1695.
Unknown. A Brief Instruction in the Principles of the Christian Religion. 15th corrected ed. London: 1747.
Unknown. A Brief Instruction in the Principles of the Christian Religion. 8th corrected ed. Boston: 1765.
Unknown. A Brief Instruction in the Principles of the Christian Religion. 16th ed. London: 1764.
Note: This edition is published with a picture of Benjamin Keach.
Beddome, Benjamin. A Scriptural Exposition of the Baptist Catechism by Way of Question and Answer. 2nd ed. Bristol: William Pine, 1776.
The Baptist Catechism. Bristol: 1784.
Rippon, John, ed. The Baptist Catechism. London, 1794.
Unknown. The Baptist Catechism as Printed by the Charleston Association. Unknown Publisher: 1813.
Unknown. Keach’s Catechism. Baptist Mission Press, Culcutta: 1833?
Notes: this document was published with a memoir to Mrs. Ann Thomas who died June 11, 1833. It has a ________ Public Library stamp with the year 1859. It has a note at the end stating, “-- printed from the London Edition at the Baptist Mission Press” So this printing of the Catechism is no older than 1833 and possibly 1859.
Beddome, Benjamin. A Scriptural Exposition of the Baptist Catechism by way of Question and Answer. Harrold & Murray: Richmond, 1849.
Unknown. The Baptist Catechism Fourth Charleston Edition. Raleigh, NC: 1850.
Unknown. The Baptist Catechism, Commonly Called Keach’s Catechism: Or, a Brief Instruction the Principles of the Christian Religion. Philadelphia: American Baptist Publication Society, 1851.
Note: this edition reproduces the following edition:
The Baptist Catechism: Agreed on by the Elders and Messengers of Upwards of One Hundred and Twenty Congregations of Christians, Baptized upon Profession of their Faith, in London, and the Country. 14th ed. Philadelphia: Andrew Steuart, 1764.