Trish,
The name could be Ballynascreen. (There certainly isn’t anywhere in the county called Balanaserinem).
This is the only McWilliams family in Ballynascreen in the 1831 census. They were RC and lived in the townland of Owenreagh.:
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Loughinsholin/Ballynascreen/Orvenreagh/20/
By the 1901 census there were 2 farms there side by side. Presumably related:
http://www.census.nationalarchives.ie/pages/1901/Londonderry/Sixtowns/Owenreagh/1544579/
http://www.census.nationalarchives.ie/pages/1901/Londonderry/Sixtowns/Owenreagh/1544580/
Only the O’Hagans were there in 1911 (Mary O’Hagan’s maiden name was McWilliams).
http://www.census.nationalarchives.ie/pages/1911/Londonderry/The_Six_Towns/Owenreagh/610715/
The baptism records for Ballynascreen don’t start till 1836, so you are not going to find any record of his birth, if that’s where he came from. Likewise of his marriage (marriage records start in 1834) or of their childrens births in Ireland. A DNA test with the O’Hagans might be about the only way of finding if there’s a connection, assuming they are still there, and willing.