It all depends upon your angle.
Louis Demar was born in Clinton County, New York, in the 1850s. He lived there until approximately 1900 when he moved to Chicago, Illinois, where he stayed through 1920. Most of the time he worked for the Pullman Car Company and it’s likely job opportunities were what brought him to Chicago. After his retirement, he returned to Clinton County, New York, in time for the 1930 census. He died in Clinton County in the 1930s.
Two of Louis’ daughters never left upstate New York and were still living there when he returned. Many of his siblings (and there were many) stayed in the Clinton County area. But three of his children left Clinton County. His two youngest daughters followed him to Chicago, raising their own families in the Midwest. His son Levi spent time in Montana and Oregon before finally settling down in extreme northwestern Wisconsin.
Researchers of Louis approach him from one of two angles–the “Illinois” angle or the “New York” angle. The angle they approach him from depends upon their relationship to him.
And that angle impacts what they know about him. It’s easy for the Illinois angle people to find him in the Chicagoland area in the 1910 and 1920 census and in city directories during that same time period. He’s living in the same general neighborhood where his two daughters are living during that time. Then he seems to disappear after 1920.
Those researching him from the New York angle, easily find him in 1860-1880 census records and in the 1930 census. He’s in Clinton County where his two daughters and numerous other family members are. It’s the intervening years where he seems to be lost. One could even conjecture that he simply was overlooked in those census years where he cannot be found or that his last name, which gets spelled Demare, De Mar, Demarrah, Dmarra, Desmarais, etc. was simply listed in a way that is not recognizable.
It is not known why Louis returned to Clinton County, New York. It is possible that after he ceased working for the Pullman Car Company in Chicago, he simply wanted to return to the more rural lifestyle in upstate New York where he had spent the first forty years of his life.
What are the genealogy lessons from Louis? Perspective obviously impacts how we research and what we know. In this case, initially Illinois researchers were missing the New York information on Louis and New York researchers were missing the Illinois information. People can “go home” after spending a decade or more in a new location, even if children live in that new location.
And the reason why we may be “missing” a person in a census year may be because that person has moved to a completely different location. It’s not always the census taker’s fault. Sometimes people move around.