Early Church Membership Records by Susan Easton Black
"Membership of the Church of Jesus Christ of Latter-day Saints, 1830-1848"
Susan Easton Black and associates researched LDS historical resources and compiled a 50-volume set of information on early members of the church. It is a good beginning point to identify available information and sources for an early LDS ancestor. It is available in hard copy in the Family History Library and Brigham Young University collections and is also available digitally. While this compilation is massive, it is not complete. It is indexed in the Early Church Information File.
"Early Members of the Reorganized Church of Jesus Christ of Latter-day Saints
Also produced by Susan Easton Black is a six-volume set titled: Early Members of the Reorganized Church of Jesus Christ of Latter-day Saints. The set is available in the Family History Library in book form and digitally. There is a preface statement that many of the RLDS membership records were destroyed in a fire at church headquarters in January 1907.