Lincoln's birthday

[Eva Elisabeth]

It just hit me to check the marriage certificate - no dates of birth either.

I still find this a very good and valid question - how do we evidently know of the date of birth respectively how was the information preserved and carried on in an illiterate world at the frontier till Abraham Lincoln was old enough to memorize himself?
Not that I mean to compare but I've serveral times experienced that new refugee students from somewhere in Africa or Mid-East didn't know their date of birth (nor their illiterate parents) and couldn't say more than "sometime ten or eleven yrs ago".