Take a look at my family tree information:http://trees.ancestry.com/tree/6709803/family
Browse up the chain following Whm Henry McFarland and his paternal ancestors as such; you should hit what I've managed to find about Thomas and Lettie, but I don't have too much more information other than listed, except I suspect that Thomas MAY have come from Washington County, NY... or was born there... or set up roots there after he emigrated. They then moved to Sterling, Cayuga Co., NY.
Lettie (short for Leticia, I believe...) had a surname of McFadden. If you look at census records of Sterling (also seen as Red Creek or Red Cord, Cayuga, NY), you can see that the McFadden's and McFarlands live close together and ingtermingle as such.
My (my wife's that is...) lineage moved westward to oregon in 1890's, with William Henry McFarland marrying Nancy Bell(e) Coffey.
Hope that this has helped. How are you related to Thomas? Perhaps we can help each other? Looking forward to hearing from you.
Robert Marx Jr.