Greetings! I'm also a descendant of Thompsom Poplett through his daugher Margaret, her daughter Mary Giles, her daughter Mildred Yates, her son Giles Crabtree to me. Margaret England (who also posted to your original query) is my father's first cousin.
I may have some more to add to what you have as to where Thompson Poplett lived/moved. This information was taken from the book "Portrait and Biographical Album of Peoria County, Illinois" from 1890. One of the people listed in this book is Wyley Poplett, another son of Thompson Poplett.
In the sketch, it says that Thompson Poplett & Jane Montgomery after leaving Kentucky, first moved to Parke County, Indiana (no date given), and then to Knox County, Illinois in 1835. They them moved to Peoria County, Section 5, Richwoods Twonship in 1846.
Wyley Poplett is listed as being born in Parke County, Indiana on June 29, 1830.
One thing that I'm not clear on is where Margaret Poplett was born. She was born in 1828. The 1850 census lists her (now as Margaret Giles, wife of Thomas Giles) place of birth as Ohio. The 1860 Census lists her place of birth as Indiana which sounds right to me. I have no other reference to the family spending time in Ohio.
Let me know if I can be of further help. I'm not familiar with Poplett Hollow, where is it located?