"Polly" is usually a nickname for Mary. Your Polly Clair is Mary Claire Logan. I have this information from more than one source, including an interview for a newspaper by her grandson who was a judge in Corinth, MS. I show 7 children for Matthew Logan and Sarah Fleece: John B. Logan ( I have no b&d dates for him, but show he married Clarisa D. Finch on Oct. 7, 1851) Robert Logan (no other info)  Mary Claire Logan ( I did not have a birth year for her, but your date of 1811 fits very well and I add that to my data; she married Mar. 26, 1829 to John Waller Johnston, and she died Feb. 1843 in Adair Co., KY.)  James Logan (b. Apr. 10. 1813, d. Sep. 15, 1878, married Oct. 7, 1862 to Sallie Harber)  Maria Jane Logan )b. 1820, married Aug. 27, 1877 to George Phillips)  Henry Logan (b. 1825, d. 1898; buried in Johnston family cemetery, Adair Co., KY)  Diana Logan ( b. Bible record says May 3, 1827,epitaph says born May 9, 1827, died Dec. 16, 1912, married May 30, 1843 to James Lawrence Johnston.
Mary Claire Logan was oldest daughter and married John Waller Johnston, oldest child of Thomas Buford Johnston and Sarah Ann Dawson. Diana Logan was youngest daughter and married James Lawrence Johnston who was youngest brother of John Waller Johnston and the 7th child of 9. James inherited his father's plantation and was born, lived and died there. The house which Thomas Buford Johnston bought from Green Casey is still standing and occupied in Adair Co., KY just north of Columbia, KY. It is no longer in the Johnston family, but the Johnston cemetery is still on the property. Some years ago the "Purchase Parkway" was put through the middle of the old Johnston farm and most of it was sold off. A descendant of James and Diana still lives on a small part of the old family farm south of the parkway. She has the family Bible of James L. Johnston and also provided a picture of Thomas Buford Johnston. After Sarah Ann Dawson Johnston died, T. B. Johnston married the widow Sarah Fleece Logan. They did not have any issue.