He did join the membership class, and it was recorded on the books; it didn't last long because someone recognized him and the character he represented & sought to have him removed prior to full recognition as a member.
Wesley P. Walters, after doing some digging 36 yrs. ago, came up with info that was then published by the Utah Christian Tract Society (7&8/71 newsletter):
..."Perhaps the death of his first-born son on June 15, 1828 induced him to seek membership in the Methodist Church to which his wife belonged since she was seven years old. The 'prophet' Joseph's role as a Methodist member did not last very long, however, only three days--according to statements made by his wife's cousins, Joseph and Hiel Lewis. In their local newspaper at Amboy, Illinois, they told of their earlier years with Joseph Smith in Pennsylvania and of his uniting with the Methodist class: "'He presented himself in a very serious and humble manner, and the minister, not suspecting evil, put his name on the class book, in the absence of some of the official members.' (THE AMBOY JOURNAL, April 30, 1879, page 1.).
"When Joseph Lewis, who was 21 at the time (about a year and a half younger than Smith), learned of this act, he felt that Joseph's manner of life rendered him unfit to be a member and told him either to 'publicly ask to have his name stricken from the class book, or stand a disiplinary investigation.' Mr. Lewis gave further details about the incident a month after the first article appeared in the Amboy paper, and he wrote: "'I, with Joshua McKune, a local preacher at the time, I think in June, 1828, heard on Saturday, that Joe Smith had joined the church on Wednesday afternoon, (as it was customary in those days to have circuit preaching at my father's house on week-day). We thought it was a disgrace to the church to have a practicing necromancer, a dealer in enchantments and bleeding ghosts, in it. So on Sunday we went to father's, the place of meeting that day, and got there in season to see Smith and talked to him some time in father's shop before the meeting. Told him that his occupation, habits, and moral character were at variance with the discipline, that his name would be a disgrace to the church, that there should have been recantation, confession and at least promised reformation--That he could that day publicly ask that his name be stricken from the class book, or stand investigation. He chose the former, and did that very day make request that his name be taken off the class book.' (THE AMBOY JOURNAL, June 11, 1879, pg. 1).
"Mr. Lewis' more detailed statement was called forth because the original statement he and his brother had made had been challenged by a local Mormon elder from the Reorganized Church. This elder, Mr. Edwin Cadwell, was a neighbor of Mr. Michael Morse, the brother-in-law of Joseph Smith. Mr. Cadwell stated that Mr. Morse told him that 'Smith's name remained on the class book...for about six months, when it was simply 'dropped' as Smith did not seek to become a full member.' (THE AMBOY JOURNAL, May 21, 1879. pg. 1).
"Mr. Morse had been the 'class leader' at that time and had been the one who had taken Smith's name for recording in the class book. (THE AMBOY JOURNAL, July 2, 1879, pg. 1). To the statement of Mr. Morse, Joseph Lewis replied that, 'If said Morse was a leader at that time, and Smith's name remained on the class book six months, the class leader carelessly or wickedly neglected his duty.' (THE AMBOY JOURNAL, June 11, 1879, pg. 1).
"Like so many of the early Methodist records, the early class books of Harmony (now Lanesboro) Church are lost, so we will never know for certain whether Joseph Smith remained a member for only three days or for six months."
Three whole days he was among them?
Gotta wonder how many he tried to tempt and corrupt in that time.