I do see the name "Robert Sayres" crossed out just above Polly Roberts' name on the 1840 census. I'm not sure what to make of it, but I think it's at least a good possibility that Robert may have had a connection to Polly Roberts. It's a clue, but you'll probably still need to find more to substantiate your speculation.
I found two other sources that I'm not sure if you had located already. One was Dennis E. Roberts' Findagrave memorial page at https://www.findagrave.com/memorial/43471592/dennis-e-roberts,
which gives his death and burial locations -- I'm not sure why there isn't a photo of his headstone, and that makes me wonder about how much to trust the information given there. There is also an entire "Roberts Cemetery" at https://www.findagrave.com/cemetery/2437981/memorial-search?firstName=&lastName=Roberts&page=1#sr-85126488
, where Dennis and many Roberts family members are buried.
I also located an 1870 US census with Dennis and his wife and children on it. It states that he was born in Kentucky. I was hoping it would say where his parents were born, but it doesn't. It at least tells you they lived in Kentucky at the time of his birth, if the information is accurate..
"United States Census, 1870," database with images, FamilySearch (https://familysearch.org/ark:/61903/3:1:S3HY-6Q9W-PTS?cc=1438024&wc=92K1-C6N%3A518657901%2C519293601%2C519832601
: 22 May 2014), Kentucky > Pulaski > Harison > image 15 of 44; citing NARA microfilm publication M593 (Washington, D.C.: National Archives and Records Administration, n.d.).
Dennis Roberts 1870 Male 42 White 1827-1828 Kentucky 15
Manerva Roberts 1870 Female 37 White 1832-1833 Kentucky 15
William T Roberts 1870 Male 18 White 1851-1852 Kentucky 15
James H Roberts 1870 Male 16 White 1853-1854 Kentucky 15
Julia Ann Roberts 1870 Female 15 White 1854-1855 Kentucky 15
Columbus F Roberts 1870 Male 12 White 1857-1858 Kentucky 15
Susan E Roberts 1870 Female 10 White 1859-1860 Kentucky 15
(next image on same census, continued)
Greenberg Roberts 1870 Male 6 White 1863-1864 Kentucky 16
Charity A Roberts 1870 Female 5 White 1864-1865 Kentucky 16
Mary Jane Roberts 1870 Female 3 White 1866-1867 Kentucky 16
Martha E Roberts 1870 Female 1 White 1868-1869 Kentucky 16
There is also a family of Tarters (and a Brown) in the household immediately next to (before) the Roberts family on the census.
This doesn't help much with your question about Polly, but I hope you can find some additional clues. (Here's the link):
Did you see this previous question that *may* be connected to your Polly? https://www.wikitree.com/g2g/356956/can-anyone-help-me-with-finding-mary-polly-tarter-husband