The following data have been extracted from the 1810 to 1840 census records for the household of Abner Willis. It is assumed that he is the eldest male listed in these records.
The above data give age ranges for Abner Willis in various census. These census' used varying reporting ranges in different years. The overlap in the ranges between different years can allow us to infer, or at least narrow, Abner's likely year of birth.  From these data it appears that Abner could have been born nor earlier than 1775, and no later than 1780.