1 Ancestor + 1 Census can = 2 Locations

Check when census was taken. Example: Ohio census might be taken in April, 1860 and Illinois census taken August, 1860; and your ancestor might have moved from Ohio to Illinois in May, June or July of 1860, the result; their being listed in both censuses.

Document, Document!

Always cite your sourses, not only to remember what records/books you have searched to avoid backtracking: but also to avoid any copyright infringement problems!!

LOST ANCESTOR?

Sometimes you cannot directly find your ancestors. We recommend you go to a second or third cousin, who may lead back to a brother/sister. This possibly, may lead you to your "lost" ancestor. This is known as indirect or "backdoor" research.