Or, in my case, the Danish equivalent of John Smith: Jens Jensen, my paternal great-grandfather.
I know almost nothing about him: he came to the United States in 1900 with my great-grandmother, Thyra Amalia  Martinsen, and their son Oscar; by 1910 , he was farming in Platte, Nebraska and supporting a family of five–wife Amelia, and children Oscar (10), Johanna (7), Marie (6), and Florence (3); by 1920 he has disappeared–separated from my great-grandmother, perhaps divorced. There are stories of his drinking and squandering of money.
And that is where the trail ends.
To find out more about Great-grandfather Jens, I need to know who his parents are. But, in Denmark, that’s easier said than done.
Until the mid-nineteenth century, Denmark operated using a naming convention: sons took on a surname made from the father’s first name with the suffix ‘sen’ added, while a daughter’s surname was the father’s first name with the suffix ‘datter’ added.
So, every Jens born in Denmark had children with the surname Jensen or Jensdatter. So Jens Neilsen’s son would be a Jensen. And Jens Andersen’s son would be a Jensen. Even Jens Jensen’s son would be a Jensen.
Even the Danes became confused with this scheme, so in 1828, they decreed that surnames would remain fixed. If you were born a Neilsen, your sons and daughters would be Neilsens. Unfortunately, the decree wasn’t strictly adhered to, especially in rural areas. 
I didn’t fully understand this naming convention when I found the below 1880 Danish Census record.  I was excited that I’d found my great-grandfather’s family. But, in truth, without knowing Great-Grandpa Jensen’s father’s name (first and last), there is little hope of unequivocally finding him. 
Looking more closely at the Danish naming convention, this time applied to first names (and assuming that my great-grandparents adhered to this convention), there are, perhaps, additional clues.
- The first male child was named for the father’s father = Jen’s son Oscar
- The first female child was named for the mother’s mother = Johanna
- The second girl was named for the father’s mother = Marie
- If a child died, the next child of the same sex was usually given the same name. 
So… I’m looking for a Jens Oscarsen or an Oscar Jensen. Perhaps married to a Marie. Depending on whether the family ignored the decree to keep last names constant or not, as well as how well they followed the rules for Given Names.
Or maybe somebody completely different. 
Geez! My head hurts!
Please, won’t the real Jens Jensen just take one step forward?
Sources & Notes
- My great-grandmother’s name changes depending upon the record one views: Thyra on the Immigration Passenger List; Amelia in the 1910 Census; Amalia in the 1920 Census; 1930 & 1940 Census (Censi?), along with several local Directories all list Amelia; Social Security has her as Amalia; Find-a-Grave has her as T. Amalia.
- Source: 1910 United States Federal Census
- See Denmark naming conventions
- You can see the digital version of the record here: 1880 Denmark Census; Translations (from Google Translate)
- Husfader = husband
- Gaardmand = yard man, gardener
- Aftægtsmand = pensioner
- Hans hustru = his wife
- Deres barn = their child
- Tjenestedreng = service boy
- There is some hope of finding him… if I can find, and persuade, first, second and third Jensen cousins (i.e. descendants of Marie and Florence Jensen, since Oscar had no children) to take DNA tests. And then only if some relatives remaining in Denmark have taken them as well. So… a long shot.
- This is pertinent because my handwritten Martinsen family notes say that my great-grandparents had six children, only four of whom lived to maturity.
- Because in 1850, the Danes changed the law again, allowing people to take non-patronymic names that reflected their jobs or where they lived… like Miller… or Tailor.