You just “know” that your ancestor was residing in that county in 1860!  Where is he?

It could be that you ancestor was missed – his information was not recorded. There are various reasons for this possibly happening. If he was not at home when the census taker arrived, a neighbor may not have known much about him – his real name, what his age was, etc. Another reason is that your ancestor may have been avoiding the census – for some reason he did not want to “be found”. I am sure that there are many other reasons that he may not “be there”.