In addition to LiveDove's explanation, some of the census takers themselves were semiliterate. A number of years ago I read in a census index, (think it was OH, but can't remember the year), a disclaimer to the effect that the census taker was drunk when he took the census, so proceed at your own risk. In one of the censuses, my great-grandfather is listed in two different counties. They are adjacent, so I don't know if one of the census takers just strayed over the county line, or if the family moved between one survey and the other. Also, my grandfather's name which was Joab, was listed as Job. Censuses are very helpful, but are NOT infallible. Use them as an information source for further research. Barbra