And to expand on what's already been said:
You have to be very careful about just using data in the indexes in ancestry.com. Indexers often don't pay much attention to the characteristics of the handwriting of particular census takers and tend to guess that names which they aren't familiar with are more modern names. So you often need to check the actual census record, not just take the data presented in the index at face value.
For example, when I was doing research on the use of
Pearl as a given name, I saw there were several supposed examples of women named
Pearl who were born before 1850 in the ancestry.com indexes of the US census. When I checked to photocopies of the original census records, every one of these turned out to be a mistake -- most commonly the indexer read the now-rare New Testament name
Persis as "
Pearl". It turns out there really are no women named
Pearl in the US census born before
Nathaniel Hawthorne's novel "The
Scarlet Letter" was published in 1850, but you would think there were if you just relied on the indexes.