Inconsistent birth dates with my Irish ancestors?

Trust nothing but baptismal records* and death certificates to establish dates. http://www.ancestry.com/wiki/index.php?title=Overview_of_the_U.S._Census#Problems_with_Accuracy People commonly mis-reported their own ages (intentionally) and the ages of members in their family (unintentionally); enumerators commonly made up ages, lost ages on scraps of paper and then made them up, or had such poor handwriting that correct ages were lost in transcription. In other words, the situation you describe is common, is not restricted to the Irish in any way, and indicates nothing more than that the US Census is an unreliable store of individual data. *As I'm sure you know, there were no birth certificates in Ireland before 1864.

I have lots of Irish relatives born around the turn of the last century that played with the year of their birth when seeking employment or marriage. Record keeping was not as strict as it is today and I think offhand of two relatives that were born in the 1890's that adjusted their age one by five years one by ten. The only people that knew the truth eventually die off. There's the story of a great aunt that met a marriage prospect, asked him his age and then adjusted her age to be a year younger, rather than the five to six years older that she was. Also stories of those who had gone to England to work and then adjusted their age to emigrate to the US or Canada.

I'm not sure if this is true for Ireland, but I've found that baptism dates can be a while after actual birth dates. It varies in my family by anywhere from a month to (we think) years after the actual dates of birth for relatives born in the 1800s. In one family of 9 kids, there are a couple "clusters" where they got two or three baptized at the same time, I suppose because it was convenient.

I think your common factor there is that the date of birth on tombstones and obituaries are obtained from relatives, who may well not have had access to the birth or baptismal records you're looking at. I'm not sure I could remember the exact year of my grandparent's birth off the top of my head.

I have an Irish ancestor that came over pretending to be an adult when he was 14 or so--this was family lore that was borne out in records with a variable early 19th c. birth date. The census was taken with whatever adult happened to be in the house at the time; it could have been (to take an example I've seen) a person who ran the boarding house that guessed that a recent tenant was about 40 years old. Also-also, I have news clippings from the mid-late 1800's with all kinds of inaccuracies, and someone who died at 52 vs. 56 just doesn't seem like the level at which they did a lot of fact checking. They spell my family's last name two different ways in one article, both incorrect.

Diablevert points to one factor. The census records are different, presumably you refer to self-reported or parent-reported information there. My guess would be that this family came over without bringing copies of baptismal certificates or any other information, and that over time they simply forgot the correct dates. Also, since they were all baptized in Ireland the family presumably came over here after 1844, and they may have wanted the kids to start school in a grade below their age level so they misrepresented the birth dates by a few years and it stuck. Finally, infant mortality was high, so it's possible, for example, that Mary1831 died and a child born 1833 was named Mary again. Also, what valkyryn said.

Name similarity is also a culprit, as beagle notes above. With my Scottish ancestors, for example, the first-born would be named after the grandfather, so you'd have three or four 'Donald McLeans', all born in the same parish and all within a few years of each other. Donald McLean, born 1753, may or may not be the same person as Donald McLean, born 1755.

In Dutch families it's very important to pass specific names down. My grandfather had 3 brothers named Johannes. The first Johannes died as an infant so they named the second son Johannes when he was born. He lived, so they named the third son Martin. Then Johannes 2 died at age 4, so they named the fourth son Johannes. Is it possible this is part of your puzzle?

Three possibilities, all of which I'vecome up against over and over in my own family searches: • honest mistakes --- this can include anything from someone not being sure of their exact birth date to bad handwriting ("is that 1833 or 1838?!?") to mishearing on the part of the census recorder. • lying --- lying that they were older, to pass as an adult; lying that they were younger, maybe to avoid the draft or enter school. • duplication within the family --- some families liked to reuse the same names for religious reasons (all the girls might get first name like Marie, all the boys might get named for the same saint). Or, as someone notes above, because of the higher infant mortality subsequent kids might be named after a deceased older child.... for example, there's one family in my maternal lines that had at least fifteen children; of those fifteen, three boys were names Johannes, two girls named Barbara, two named Catherine, and FIVE named Anne, all because so many died very young.