Zachariah Allen in Greene Co., Illinois was not Zachariah Boone Allen.Zachariah Allen b. 1760 Rowan Co., North Carolina moved to Davidson Co., Tennessee in the late 1790's.In 1819 he moved from Davidson Co., Tennessee to Greene Co., Illinois entering land very close to White Hall, Illinois.
According to Pike Co., Illinois History Zachariah Boone Allen moved there about 1820 and died shortly after.
A Y-DNA test is in the process of being taken on an Allen male who is the great-great grandson of Zachariah Allen b. 1760, Rowan Co., North Carolina.I hope this test provides some answers.