Basic Genealogy: Estimating Birth Dates

In those situations where we do not have a birth date for an ancestor, family historians must rely upon other sources of data to obtain an approximate year of birth. There will be times when this is the best that we can hope for in these situations.

One of the sources for approximating a person’s birth year is the decennial census that is taken in the United States and other countries. In the US, the census is taken in the year that ends the decade – which is the year that ends in zero.*

Theoretically, a person should increase in age 10 years with every census; however, this is not always the case. There a couple of reasons why this may happen.

1. The person giving the information may not really know his or her age or birth date. In our society, where our birth date and Social Security Numbers are necessary information, this seems unfathomable. A birth date/and or age was of lesser importance in the past.
2. A person may have temporarily forgotten his or her own age while giving the information to the census taker. Think about how many times a person in your presence was confused about his or her age.
3. The person giving the information to the census taker was not the person in question and provided incorrect information based on their own level of knowledge of the other individual.
4. The date from which ages were to be calculated changed over census years and variations may be related to this factor. In each census, a specific date was given to calculate the person’s age. For example, several censuses registered the age as of June 1 of the census year. If one person was born on May 28, 1850, he would have been registered at being 10 years of age in the 1860 census. Another person born five days later on June 2, 1850 would be listed as 9 years old. The following chart provides the date when census age was to be calculated.

Census Year	Age by Date
1790	First Monday in August (2)
1800	First Monday in August (4)
1810	First Monday in August (6)
1820	First Monday in August (7)
1830	1 June
1840	1 June
1850	1 June
1860	1 June
1870	1 June
1880	1 June
1880	1 June
1890 Fragments	1 June
1900	1 June
1910	15 April
1920	1 January
1930	1 April

There are several other factors to consider when checking the census records for age. The censuses prior to 1850 did not provide an exact age, but rather a range of ages. These first six censuses also only listed the head of the household.

The 1890 is virtually missing, as the vast majority of these census records were destroyed in a fire. Some isolated record fragments exist for certain locations; however, for the most part, the 1890 is nonexistent.

The 1900 census also provided the month and year of birth in addition to the person's age. The 1900 is valuable in this regard. Unfortunately, these two records sometimes do not always agree for a variety of reasons including error.

Considerations:

To approximate an ancestor’s year of birth, it is necessary to chart the age of the person over several censuses.

In the past the genealogical community used a legal term, the preponderance of the evidence, to describe the totality of the evidence to make a reasonably correct assertion about our ancestors.

As the term has been discontinued for genealogical purposes, Helen F.M. Leary argues “The genealogical standard applies when evidence is direct and virtually impregnable (e.g., an interlocking series of birth, marriage, and death certificates, for example). It applies when circumstantial evidence is assembled—to distinguish among several persons of the same name, perhaps. And it applies when evidence is insufficient for a solid case, because records do not survive or were never created.”¹

Several benchmarks can be assumed in making a hypothesis regarding aspects of one’s family.

1. Eyewitness accounts are generally weighted as being more accurate. (i.e., a parent’s statement about a child’s birth date is more reliable than another relative who was not present at the person’s birth).
2. Information recorded at or closer to the time of the event generally holds more weight than documentation created years after the fact. (i.e., a birth certificate’s record of a birth date is more reliable than a person’s death certificate that records a date of birth).
3. Primary records are generally more reliable than secondary or tertiary sources. Actual records of an event, such as marriage certificates, are more reliable than a local history book that notes the date of a wedding.
4. Even though certain evidence (as noted above) appears to be stronger, mistakes can and do happen within this documentation (i.e., incorrect information on a birth record).
5. In some cases, weaker secondary data may be the only record of an event; hence, this may be the only useful piece of evidence that is available and must be used.
6. While assumptions can be made, all evidence needs to be considered, analyzed, noted, and the sources of the evidence documented.

Examples:

For illustration purposes, I have picked three ancestors for which I do not have an exact date of birth and charted these as they appear in the various census records.  In the 1830 and 1840 censuses, only a range of ages are given and only the heads of households are named. The exact identity of each household member cannot be verified but only speculated by using other data; often, you will find a spurious person whose identity is beyond speculation.

Henry Brakeall - my 3rd Great Grandfather
Census Year	Location	Listed Age	Birth Date Range
1840	Warren Township, Franklin County, PA	30 to 39	June 2, 1800 – June 1, 1810
1850	Thompson Township, Fulton County, PA	45	June 2, 1804 – June 1, 1805
1860	Liberty Township, Clinton County, OH	57	June 2, 1802 – June 1, 1803
1870	Washington Township, Clinton County, OH	66	June 2, 1803 – June 1, 1804
1880	Washington Township, Clinton County, OH	76	June 2, 1803 – June 1, 1804

With my first example, the 1840 information only confirms the general time of when Henry was born.  While the ages and the resultant dates vary, only two of the four records agree:  the 1870 and 1880 censuses.  I believe that we can conclude that Henry was probably born during 1803 or 1804.  I have seen a number of unsourced genealogies that state that he was born on July 1, 1804; however, since no citations are listed, the date should remain suspect.  Henry appears to have been born circa 1803 or between 1803 and 1804.

Susan Brakeall - my 3rd Great Grandmother
Census Year	Location	Listed Age	Birth Date Range
1840	Warren Township, Franklin County, PA	30 to 39	June 2, 1800 – June 1, 1810
1850	Thompson Township, Fulton County, PA	48	June 2, 1801 – June 1, 1802
1860	Liberty Township, Clinton County, OH	59	June 2, 1800 – June 1, 1801
1870	Washington Township, Clinton County, OH	68	June 2, 1801 – June 1, 1802

For Henry's wife Susan, there are only three usable census records (1850, 1860, and 1870). Of the three, two agree that she was born in either 1801 or 1802. In applying an approximate birth year, I might list it as circa 1801 or between 1801 and 1802.

John Merriman - my 2nd Great Grandfather
Census Year	Location	Listed Age	Birth Date Range
1830	Ohio Township, Allegheny County, PA	0 to 4	June 2, 1825 – June 1, 1830
1840	Ohio Township, Allegheny County, PA	10 to 14	June 2, 1825 – June 1, 1830
1850	Pittsburgh Ward 2, Allegheny County, PA	24	June 2, 1825 – June 1, 1826
1860	Allegheny Ward 2, Allegheny County, PA	30	June 2, 1829 – June 1, 1830
1870	Allegheny Ward 3, Allegheny County, PA	40	June 2, 1829 – June 1, 1830
1880	McKeesport, Allegheny County, PA	50	June 2, 1829 – June 1, 1830

For John Merriman, three out of four censuses agree that he was born in either 1829 or 1830. So he might be listed as being born circa 1829 or between 1829 and 1830. The disagreeing census record has John living in a hotel with a number of other residents. It is possible that someone besides himself provided the information.

As for your own ancestors, hopefully the evidence will lead you to make a reasonable assumption regarding a year of birth for some of these individuals.


¹Leary, H.F.M. (1998, January) Evidence revisited: DNA, POE, and GPS. OnBoard 4(1).