Perhaps the following will help jog your grandfather's memory.
Joseph N. LeCompte, born April 1850 in Dorchester, married Jennnie Hurley, daughter of Alexander Hurley and Sarah Fleming. They resided in Vienna and had at least 7 children: Nettie, Ella, Marie, Blanche, Jesse, Elwood, and Percy.
I don't know if this Percy is your H. Percy LeCompte or not, but seems very likely. There is also a walking tour of Vienna, MD that mentions the Percy LeCompte House. Is this your Percy? I do know that a Percy LeCompte (b. abt 1895) married Olga Kemp (b. abt 1897) on 26-Feb-1916 in Vienna. Olga was the daughter of Edward F. Kemp and Erma.
Percy's sister, Blanche, married a Dawson, and has grandchildren living in MD, including Mark Johnson. Blanche died in 1972.
Path back to immigrant is Percy > Joseph > Solomon > Moses > Moses > William > Moses > Antoine.
Joseph's middle name was probably Nicolls, as we he was the son of Solomon S. LeCompte (b. 1821) and Henrietta R. Nicolls (b. 1827). His sisters were Mary Hester, Ella, and Annie.
Solomon was the son of Moses LeCompte (1788-1837) and Mary Shearman (abt 1796 - aft 1850) who married in May 1, 1815 in Dorchester. Solomon's siblings were Eliza Ann, Thomas J., Stephen Barnett, and Deborah.
Moses was the son of Moses LeCompte (b. 1762) and Elizabeth Wheeler (b. abt 1760) who married June 11, 1782 in Dorchester. His siblings were Mary, Mahala, and Hugh. Hugh is my ancestor (see www.lecompte.net).
The sources for the above information include the obituary of Robert M. Hurley, the 1850 and 1860 Census, the family Bible of Hugh LeCompte, DCGM index, and "Revised History of Dorchester County Maryland" by Elias Jones (Read-Taylor Press, Baltimore, 1925).