No - I don't know for sure which County in Pennsylvania that my James Alexander was born in. His Rev War Pension Application stated that he was b. 1749 in Pennsylvania. He also stated that he joined the Army in 1776 in Chester County, PA. Most of my effort to place him geographically has been spent in Chester County. But Chester County at one time encompassed what became Lancaster - so eventually I will probably have to widen my search.
The Rev War soldier named Reuben Alexander in Washington County, IN was not mine - my Reuben was not born until 1774 (much too young to be a soldier ).
In the 1840 Jackson County, Indiana census there were Edwin Alexander and Alford Alexander who lived next door to each other. They are part of my family - sons of Reuben and grandsons of James b. 1749 PA. By 1850 Alford had died and his widow m2 Reuben Alexander, son of Reuben but they had left Indiana. Edwin had also died but his widow, Cynthia, and their many children were still living in Jackson County, Carr township.
In the 1850 census is that your line:William Alexander 29 yo [b.1821] in KY with wife, Sally 21 yo b. IN and child, Thomas A. 2 yo [b. 1848] IN? There is also John Alexander 40 yo [b. 1810] KY and wife Frances. Children were John H. 6 yo b. IN and Isaac 6/12 yo b. IN. Next door to them is an interesting family (even more so since you've told me that Thomas' second wife was a King):
Nancy Hutchison 43 yo b. KY Rebecca Hutchison 14 yo b. IN Elizabeth King 45 yo b. KY Mahala Alexander 5 yo b. IN Louisa J. Alexander 3 yo b. IN
By 1860 these two Alexander girls (Mahala and Louisa) were living with John & Frances Alexander and son, John H. but Isaac seems to not be there - perhaps died young?
I once had correspondence with someone who descended from Mahala (I think that was the one) and if you think that this family is related to yours, I would be happy to put you in touch with her.
I understand about grabbing at straws. . . . . . with these difficult ancestors I think we sometimes have to use some very creative thinking in the search for real data that will prove the link!