Janet,I hope you're not relying on the Horn book for information on Longs.
Maud Horn's Atchley family history : including Long, Maples, Scoggin, and Griffith families was first published in the late 1930’s. Mrs. Horn did a great deal of work collecting information on all these families and her work continues to be a useful resource. However, the book relied often on hearsay in the form of letters from descendents - sometimes three or four generations removed from the persons discussed with little or no effort given to verifying the information. As a result the book is reasonable accurate regarding the generation that was living when it was published, but is less and less reliable with preceding generations.
An example is the family of Rev. George W. Long 1771-1849 and his wife, Elizabeth Maples.
1). Mrs. Horn identifies Rev. Long’s parents as John Long and Mary Haynes. She says that John Long married Mary Haynes in Bedford County, Virginia, but lists no date. She says George Long was born in 1771. -- Recorded in Bedford County, Virginia, under date of August 3, 1772, is the marriage of John Long and Mary Haynes. Stephen Sanders, surety. Consent of Mary herself. This is a year after George was born. In addition, John Long and Mary Hanes removed to Woodford County, Kentucky where they appear in census records until their deaths. John died there in 1832 leaving a will in which he names all his children, and there isn’t a George listed.
2) Maud Horn says that during his boyhood George Long came with his parents to Tennessee to settle in the northern part of Sevier County. There he married during 1793 to Nancy Maples. - - George Long and Elizabeth Maples were married 9 Jun 1791 in Pittsylvania County, Virginia. George appears in the 1800 census there. He came to Sevier County when he obtained a land grant in 1807 along with members of the Maples and Atchley families. All of his children who were born prior to 1806 show their birth place as Virginia in census records.
3) Maud Horn says that George’s father, John Long , built an overshot watermill and after his death the mill was operated by his son-in-law, Thomas Langston, who had married Nancy Long. - - Thomas Langston was first married Louisa Atchley 10 Jan 1833,in Sevier County, Tennessee when he was 19 years old, and then to Amy O. Atchley in 19 May 1861 in the same county. There is no indication that he ever married Nancy Long, or that he ever had a wife named Nancy. He does list his occupation as Miller in census records beginning in 1860. His father-in-law at that time was an Atchley, and there is a record in 1861 of an Atchley Mill in Sevier County.