You may be correct that there are two Samuels (or more) whose records are being mixed up together. The history that I am fairly sure of is the following:
Daniel Stillwell moved to Green Co KY circa 1795 and was on the 1795 Tax list for Green Co KY. He was on the Adair Tax List in 1798. Daniel and family is found on the 1810 Census Adair County KY with wife, 4 sons, and 3 daughters. Daniel's wife was Eleanor. Their children were James, Polly, Abraham, Malinda, Isaac, Jacob, and Ennis. Daniel died December 1813 in KY. Widow and children moved to Morgan County Illinois with Thornton Sheppard family circa 1830.
Isaac moved to Green Co KY circa 1795. Married Elizabeth Howell 1798 in Washington Co KY. Isaac is in the 1820 Census Hardin Co KY with wife, 3 daughters and 5 sons. Isaac also lived in LaRue Co KY and many of his descendents still do. The Stillwell Family Cemetery, LaRue County, is on the Howardstown Map, Sec 16-M-48 Carter Coord, 2 miles NW of Levelwoods on Sadie Brewer farm.
Elijah moved to Green Co KY circa 1795. Elijah was on 1810 Census Adair Co KY. Elijah wrote a Will Dec 4 1845 Adair Co. KY. Elijah's children were Nancy, Rachel, John, Sarah, Elijah Jr.,Jemima, Elizabeth, and a son Jennings (possibly Hiram Jennings). Jemima has more information posted on the various Web sites.
Reportedly these three brothers also had siblings Samuel Jr., Joseph and Rachel. The father is Samuel Stillwell.
Now here is the confusion: A Samuel is reported in Westmoreland County which is WEST Pennsylvania. A Samuel is reported in Bucks County which is EAST Pennsylvania. The BIG question is whether these are the same Person.
The WEST PA Samuel is reportedly married to Margaret Ann Hoffmire and hails from New Jersey and may be the son of Nicholas Stillwell born 1705; the son of Captain Jeremiah S. Stillwell born 1661; the son of Lieutenant Nicholas Stillwell born 1603 and Ann Van Dyck.
The EAST PA Samuel that is reported by you is married to Ann Shacklett and hails from Loudoun County Virginia. You have lots of info about this Samuel in Buck's County and in Loudoun.
Question: if these Samuels are the same man then how did (when did)EAST Samuel move from Buck's County to Westmoreland?
Another Question: what is the ancestry for the EAST Samuel going back to Lt Nicholas of New Amsterdam?
Final Question: If these are two different men then which is the father of the Adair & LaRue Kentucky Stillwells?